A plain-English glossary of carbon credit terms
Carbon credit terminology gets thrown around like everyone already knows what it means. Here's what the terms on this site — and most others — actually mean, in plain language.
Carbon credit / carbon offset
A unit representing one tonne of CO2-equivalent (CO2e) that's either been prevented from entering the atmosphere (avoidance) or removed from it (removal). Buying and "retiring" one is a claim that you've funded that tonne's worth of climate action — it does not erase the emissions you personally caused.
Registry
The organization that issues, tracks, and permanently retires credits so they can't be sold or claimed twice. Verra and Gold Standard are the two largest; Puro.earth is a newer registry focused on engineered removals. A credit's registry is the single most checkable fact about it — always look for the retirement record.
Retirement
The permanent, public act of taking a credit out of circulation and assigning it to a specific buyer, so it can never be resold or counted again. This is what actually "uses up" a credit — buying one without retiring it doesn't offset anything.
Vintage
The year the emissions reduction or removal actually happened. Older vintages are sometimes cheaper, but a stale vintage can also be a sign of unsold inventory from a project that's struggled to find buyers — vintage alone doesn't tell you quality.
Avoidance vs. removal
Avoidance credits (like clean cookstoves, or protecting a forest that would otherwise be cut) prevent emissions that would have otherwise happened. Removal credits (like reforestation, biochar, or direct air capture) pull existing CO2 out of the atmosphere. Removals are generally considered the stronger claim, but they're also usually far more expensive to verify and deliver.
Permanence & reversal risk
How durable the carbon storage actually is. A tree that burns down releases the carbon it stored — that's a reversal. Nature-based projects (forests, mangroves, soil carbon) generally carry more reversal risk than engineered removal (direct air capture, biochar, mineralization), which is one reason engineered removal tends to cost more.
Buffer pool
A shared pool of credits that reputable registries hold back — unsold — specifically to cover reversals across all the projects they certify. If one project's forest burns down, credits from the buffer pool are cancelled to make up the loss, instead of every buyer of that project simply losing their claim.
Leakage
The risk that a project just displaces the emitting activity rather than eliminating it — for example, protecting one forest while the logging operation simply moves to an unprotected one nearby. Well-designed projects account for this in their baseline; not all of them do it well.
ICVCM Core Carbon Principles (CCP)
A set of quality criteria published by the Integrity Council for the Voluntary Carbon Market, currently the closest thing this market has to an independent quality bar. A "CCP-labelled" credit has been assessed against these criteria — it's a meaningfully stronger signal than registry approval alone.
Trust Score (OpenCarbon-specific)
Our own aggregation of CCP status, third-party ratings (Sylvera, BeZero, where available), and our own review of permanence, leakage, verification quality, and co-benefits. Full methodology on how we score projects.
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