Anthropogenic activities removing CO2 from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products (IPCC WGIII AR6).
Carbon removal involves several modules: extraction from the air or upper ocean, conversion into a storable format, transportation, and storage. Carbon dioxide removal is often abbreviated “CDR”. Note that some policy environments (e.g., UK) use “greenhouse gas removal” as a broader category which contemplates the removal of GHGs other than CO2. “Carbon removal” could be interpreted to mean the removal of any GHG containing carbon (i.e., both CO2 and CH4 (methane)), but would not include the removal of other GHGs such as N2O.