Assigned amount unit. A Kyoto Protocol unit equal to 1 metric tonne of CO2 equivalent (CO2e). Each developed country (Annex I Party) has been assigned with emissions targets under the Kyoto Protocol, and a certain amount of AAUs representing the level of allowed emissions. These units, can be traded and sold under the emissions trading mechanism, and used to meet obligations under the Kyoto Protocol. (see Emissions trading)

Sources:  www.unfccc.int