The Kyoto Protocol invented the concept of carbon emissions trading, whereby carbon credits were a "flexibility mechanism". Under this flexibility mechanism Annex 1 (developed countries) could use the carbon credits to meet their emission reduction commitments. A carbon credit is a generic term for any tradable certificate or permit representing the right to emit one tonne of carbon dioxide or the mass of another greenhouse gas with a carbon dioxide equivalent (tCO2e) equivalent to one tonne of carbon dioxide.