Sustainability glossary: 50+ green terms explained

Whether you're reading a news article, a product label or a company's sustainability report, these are the words you'll encounter. Each definition is written to be honest and useful — no spin, no greenwash.

A – B

Biodegradable

Able to be broken down by microorganisms — bacteria, fungi, worms — into natural substances such as water, carbon dioxide and organic matter. Almost everything biodegrades eventually, so the word is nearly meaningless without a timeframe. A product that takes 400 years to break down under landfill conditions is technically biodegradable. Look for certified standards (such as industrial or home compostable certifications) for something more meaningful.

Biodiversity

The variety of life on Earth, at every scale — from genetic diversity within a species, to the range of species in a habitat, to the variety of ecosystems across the globe. High biodiversity means ecosystems are more resilient: more species means more redundancy, so the system can absorb shocks. Agriculture, development, pollution and climate change all reduce biodiversity.

B Corp

A certification awarded to companies that meet verified standards of social and environmental performance, accountability and transparency. B Corp status is granted by a non-profit and requires companies to balance profit with purpose and undergo periodic reassessment. It is a business certification, not a product certification.

C

Carbon capture (and storage)

Technology that removes carbon dioxide from the atmosphere or catches it at the point of emission — for example, at a power station — and stores it, usually underground in geological formations. Carbon capture is real but currently expensive and operates at a small scale globally. It is sometimes proposed as a way to continue burning fossil fuels while still meeting climate targets; critics argue this delays the shift to renewables.

Carbon-neutral

A state where the net carbon dioxide emissions from an activity, product or organisation are zero — usually achieved by a combination of reducing emissions and offsetting those that remain. Carbon-neutral claims are common but the underlying calculations and offset quality vary widely. Compare with net zero, which is a broader and usually more rigorous concept.

Carbon footprint

The total greenhouse-gas emissions caused directly and indirectly by an individual, organisation, product or event, expressed in tonnes of CO2-equivalent (CO2e). Your personal carbon footprint includes the emissions from your home energy use, travel, food and the things you buy. The concept was popularised in part by a fossil fuel company's advertising campaign, but it remains a genuinely useful measure.

Carbon offsetting

Compensating for greenhouse-gas emissions in one place by funding reductions or removals elsewhere — for example, paying to plant trees or fund cleaner cookstoves. Offsets are controversial: quality varies enormously, some projects have been found to overstate their impact, and offsetting can be used to justify continued high emissions rather than reducing them. See our full guide: Carbon offsetting explained.

Carbon tax

A fee levied on the burning of carbon-based fuels — coal, oil, gas — proportional to the carbon dioxide they release. The idea is to make fossil fuels reflect their true cost to society, incentivising businesses and individuals to switch to cleaner alternatives. Different countries use carbon taxes or cap-and-trade systems (or both) with varying designs and price levels.

Circular economy

An economic model designed to eliminate waste by keeping products and materials in use for as long as possible. Instead of the traditional take–make–dispose pattern, a circular economy keeps things circulating: products are designed for repair, reuse and disassembly; materials are recycled back into new products at the end of their life. See our full guide: The circular economy explained.

Clean energy

Energy that produces little or no pollution or greenhouse-gas emissions at the point of use. Nuclear power is often described as clean energy because it produces no direct CO2 emissions, but it is not renewable (uranium ore is finite). Compare with renewable energy. The terms are related but not identical.

Climate change

Long-term shifts in global temperatures and weather patterns. While some climate change is natural, since the mid-20th century human activities — particularly burning fossil fuels — have been the dominant cause of the changes being observed: warming temperatures, rising sea levels, more extreme weather events and shifting seasons.

CO2e (carbon dioxide equivalent)

A unit that puts all greenhouse gases on a common scale by expressing their warming effect relative to the same mass of carbon dioxide over a given time period (usually 100 years). Methane, for example, is a more potent short-term warming gas than CO2, so a tonne of methane is expressed as many tonnes of CO2e. Using CO2e allows different gases to be added together into a single footprint number.

Compostable

Able to break down into usable compost within a defined timeframe under specific conditions. Industrial compostable products (often labelled with a certification logo) require the high temperatures of an industrial composting facility and will not break down properly in a home compost bin or in the environment. Home compostable products break down under the cooler, less controlled conditions of a home heap. Neither type should go into general recycling.

Cradle-to-grave

An assessment approach that looks at a product's environmental impact from raw material extraction ("cradle") through manufacturing, use and disposal ("grave"). It is the most common framing for a life cycle assessment. Compare with cradle-to-cradle.

Cradle-to-cradle

A design philosophy and assessment framework that treats materials as nutrients in continuous cycles. Instead of ending at the grave (landfill), a cradle-to-cradle product is designed so all its materials can be safely recycled or composted back into the system. The term was coined by architect William McDonough and chemist Michael Braungart.

D – E

Deforestation

The permanent removal of forest — usually to convert land to agriculture, ranching, mining or development. Forests store large amounts of carbon; when they are cleared and burned or left to decay, that carbon is released into the atmosphere. Forests also regulate water cycles, support biodiversity and protect soils.

Downcycling

Recycling a material into a product of lower quality or value than the original, often because the recycling process degrades the material. Many plastics are downcycled rather than truly recycled — a bottle may become a fleece, which cannot be recycled again. Compare with upcycling.

Ecosystem

A community of living organisms — plants, animals, fungi, microorganisms — interacting with each other and with their non-living environment (air, water, soil, sunlight) as a system. Ecosystems provide services that humans depend on: clean water, pollination, flood control, carbon storage and food production.

Embodied carbon

The greenhouse-gas emissions associated with making, transporting and disposing of a material or product — as distinct from the emissions produced during its use. For a building, embodied carbon covers everything from quarrying the stone to manufacturing the insulation; operational carbon covers the energy used to heat, cool and power the building once occupied. As buildings become more energy-efficient, embodied carbon becomes a larger share of their total lifetime impact.

ESG (Environmental, Social and Governance)

A framework used to evaluate the non-financial performance of companies and investments. The environmental pillar covers things like carbon emissions, water use and waste; social covers labour practices, supply-chain conditions and community impact; governance covers board structure, executive pay and transparency. ESG ratings are widely used in investment but are inconsistently defined and can be gamed. See our guides on sustainable investing and ethical banking.

F – G

Fair trade

A trading arrangement and certification that aims to ensure producers in lower-income countries receive a fair price for their goods, along with better working conditions and community investment. Common on coffee, tea, cocoa, bananas and cotton. Various certification bodies exist with somewhat different standards; the best-known international standard is Fairtrade International.

Fast fashion

A business model built on producing large volumes of cheap clothing very quickly, following trends at speed and expecting consumers to replace items frequently. Fast fashion is associated with low wages in manufacturing countries, high water use, textile waste, microplastic pollution from synthetic fabrics and significant carbon emissions. The alternative is sometimes called slow fashion.

Food miles

The distance food travels from where it is grown or produced to where it is consumed. Food miles are often cited as a key environmental measure, but transport is typically a small share of a food's total emissions — for most foods, how it was produced matters far more than how far it travelled. Air-freighted food (certain fresh berries, some fish and cut flowers) is an exception where transport emissions are significant.

Fossil fuels

Coal, oil and natural gas — energy sources formed from the compressed remains of ancient organisms over millions of years. Burning fossil fuels releases carbon dioxide and other greenhouse gases that were previously locked underground. Because they took millions of years to form, they are a finite, non-renewable resource on any human timescale.

Greenwashing

Making misleading or unsubstantiated claims about the environmental benefits of a product, service, policy or company. Greenwashing ranges from subtle (using vague words like "eco" or "natural" without evidence) to outright false claims. Regulators in many countries are increasingly cracking down on it. See our full guide: Greenwashing explained.

Greenhouse gases (GHGs)

Gases in the atmosphere that trap heat from the sun, warming the planet — the greenhouse effect. The main greenhouse gases affected by human activity are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and fluorinated gases (F-gases). Water vapour is also a greenhouse gas but is not directly emitted by human activity in significant amounts; it acts mainly as an amplifier of other warming.

Greywater

Wastewater from sinks, showers, baths and washing machines that has not come into contact with toilet waste. Greywater can often be reused — for example, to irrigate gardens — with minimal or no treatment, reducing the demand for fresh water. It is distinct from blackwater (toilet waste), which requires full treatment.

H – L

Heat pump

A heating (and sometimes cooling) device that moves heat from one place to another rather than generating it by burning fuel. An air-source heat pump extracts heat from outdoor air even in cold weather and moves it inside; a ground-source pump extracts heat from the ground. Because they move heat rather than create it, heat pumps can be significantly more efficient than gas or electric resistance heating. See our guide: Heat pumps explained.

Invasive species

A non-native plant, animal or other organism that spreads aggressively in a new environment, often outcompeting native species and disrupting ecosystems. Invasive species are one of the leading drivers of biodiversity loss globally. They are introduced through trade, travel, horticulture and deliberate or accidental release.

LCA (Life Cycle Assessment)

A method for evaluating the environmental impact of a product, process or service across its entire life — from raw material extraction through manufacturing, use and end-of-life. A rigorous LCA follows defined international standards. It is the most systematic way to compare the true environmental impact of different products, but it requires detailed data and methodological choices that can affect the outcome significantly.

Linear economy

The dominant economic model of the past two centuries: raw materials are extracted, turned into products, used, and then thrown away. The phrase "take, make, dispose" describes it neatly. Most current waste problems are a consequence of the linear economy. Compare with circular economy.

M – N

Microplastics

Tiny fragments of plastic, generally defined as smaller than 5 mm. They enter the environment in two main ways: as primary microplastics (manufactured small, such as microbeads in cosmetics or pellets used in plastics manufacturing) or as secondary microplastics (formed when larger plastic items break down). Microplastics have been found in oceans, rivers, soil, air, and in the bodies of animals and humans. Research into their health effects is ongoing. See our guide: Microplastics explained.

Monoculture

The practice of growing a single crop species over a large area, season after season. Monocultures are efficient for industrial agriculture but reduce biodiversity, deplete soil of specific nutrients, make crops more vulnerable to pests and disease, and typically require more pesticide and fertiliser inputs than diverse growing systems.

Native species

A plant or animal that has evolved in or naturally inhabits a particular region over a long period, as opposed to one introduced by humans. Native species are generally better suited to local soil and climate conditions and more valuable to local wildlife, particularly as food and habitat for native insects, birds and other animals.

Net zero

A state in which the amount of greenhouse gases emitted into the atmosphere is balanced by an equivalent amount being removed, so the net addition to the atmosphere is zero. Net zero targets have been set by many governments and companies, but the credibility of plans to reach them varies greatly. See our full explanation: Net zero explained.

O – P

Passive house (Passivhaus)

A rigorous building standard that creates structures requiring very little energy for heating or cooling. Passive house buildings achieve this through very high levels of insulation, airtight construction with controlled ventilation, triple-glazed windows and careful design to maximise solar gain in winter. The standard originated in Germany and is now used internationally.

Peat-free

A term used in gardening to describe compost and growing media that contain no peat. Peatlands are important carbon stores — peat takes thousands of years to form. When peat is extracted and dries out, it releases stored carbon. Peat-free composts use alternatives such as coir, wood fibre, composted bark and green waste.

Permaculture

A design approach for human settlements and agriculture that draws on natural ecosystems and ecological principles to create self-sustaining, low-input systems. The word combines "permanent" with "agriculture" (and later "culture"). Permaculture emphasises diversity, closed nutrient loops, observation before action and working with rather than against natural patterns.

Planned obsolescence

The deliberate design of products so that they become outdated or stop working after a certain time, encouraging consumers to buy replacements. It can be technological (new software incompatible with older hardware), aesthetic (frequent style changes making older products seem unfashionable) or physical (components designed to fail). It is directly at odds with circular economy principles and the right to repair.

Pollinator

An animal — bee, butterfly, moth, fly, beetle, bird or bat — that transfers pollen between flowers, enabling plants to reproduce. Around a third of the food humans eat depends on pollination. Pollinator populations have declined significantly due to habitat loss, pesticide use, disease and climate change, threatening agricultural productivity and wild plant diversity.

R

Rainwater harvesting

Collecting and storing rainfall — typically from rooftops — for later use, usually for garden irrigation, toilet flushing or washing. It reduces demand on mains water supplies and can reduce runoff that causes flooding. Regulations on what harvested rainwater can be used for vary by country.

Recyclable

Capable of being processed and turned into a new material or product. A product being technically recyclable does not mean it will be recycled — it also needs to be collected in your area, free from contamination, and there must be a market for the resulting material. Many plastics labelled recyclable are collected inconsistently or not at all in practice. See our guide on recycling symbols explained.

Regenerative agriculture

Farming practices that aim to restore and improve soil health, biodiversity and water cycles over time — going beyond simply "sustaining" current conditions. Techniques include minimising tillage, using cover crops, integrating livestock, composting and avoiding synthetic inputs. The term does not yet have a single agreed certification standard.

Renewable energy

Energy from sources that are naturally replenished on a human timescale: sunlight, wind, rain, tides, waves and geothermal heat. Unlike fossil fuels, renewable energy sources do not run out and produce little or no greenhouse-gas emissions during operation. See our full guide: Renewable energy explained.

Right to repair

A policy and consumer movement arguing that manufacturers should be required to make products that can be repaired — by providing spare parts, repair manuals and software access — so consumers and independent repairers can fix them rather than discarding them. Several countries and regions have begun introducing right-to-repair legislation for certain product categories.

R-value / U-value

Measures of a material's thermal performance. The R-value is the resistance to heat flow — a higher R-value means better insulation. The U-value (used mainly in the UK and Europe for windows and building elements) measures how easily heat passes through — a lower U-value means better insulation. They are inversely related: U-value = 1 ÷ R-value (in metric units). See our home insulation guide for more.

S

Scope 1, 2 and 3 emissions

A framework used to classify the sources of an organisation's greenhouse-gas emissions. Scope 1 covers direct emissions from sources owned or controlled by the organisation — for example, burning gas in a company's own boilers or fuel in its vehicles. Scope 2 covers indirect emissions from the generation of purchased electricity, heat or steam. Scope 3 covers all other indirect emissions in the organisation's value chain — from suppliers, from business travel, from customers using the product, and from disposal at end of life. Scope 3 is typically the largest category for most businesses and also the hardest to measure and reduce.

Single-use

Products or packaging designed to be used once and then thrown away — plastic bags, disposable cups, straws, cutlery and food packaging are common examples. Single-use plastics in particular have been widely regulated and restricted in many countries because they frequently escape waste systems and enter the natural environment.

Slow fashion

A counter-movement to fast fashion that emphasises buying fewer, better-made garments, caring for them properly to extend their life, and choosing second-hand, repaired or responsibly produced clothing. Slow fashion reduces textile waste, water use and the carbon emissions of clothing production. See our guide: Make clothes last.

Solar PV (photovoltaic)

Technology that converts sunlight directly into electricity using panels made from semiconductor materials, most commonly silicon. Photovoltaic panels generate DC electricity which is converted to AC by an inverter for use in homes and the grid. Solar PV produces no emissions during operation and has become one of the cheapest sources of new electricity in most of the world. See our guide: Are solar panels worth it?

T – Z

Upcycling

Transforming waste materials or unwanted products into something of equal or higher quality or value than the original, rather than breaking them down and starting again. Turning old wooden pallets into furniture, or worn jeans into a bag, are examples. Upcycling keeps materials in use longer and avoids the energy cost of conventional recycling. Compare with downcycling.

Virtual water (embedded water)

The total volume of fresh water used to produce a food, product or service — including the water consumed during growing, processing and manufacturing. It is "virtual" because it is not present in the final product but was used along the way. Beef requires far more virtual water than vegetables or grains, and a cotton T-shirt requires a substantial amount of water to produce.

VOCs (volatile organic compounds)

A broad group of carbon-containing chemicals that evaporate easily at room temperature. In the home, VOCs are emitted by paints, varnishes, solvents, adhesives, cleaning products and some building materials. Some VOCs are harmful to human health; they also react in the atmosphere to form ground-level ozone, a pollutant. Low-VOC and zero-VOC paints and products are now widely available as alternatives.

Zero waste

A philosophy and goal of reducing the amount of waste sent to landfill, incineration or the ocean as close to zero as possible by redesigning how products are made, used and recovered. In practice for households it means reducing consumption, buying things with less packaging, reusing, composting organic waste and recycling what remains. Strict zero-waste living requires significant effort and access to alternatives; "low waste" is a realistic goal for most people.