EVAP Canister
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
The EVAP canister is filled with carbon pellets used to absorb and store fuel vapors. Fuel vapors are stored in the EVAP canister until the PCM determines that the vapor can be consumed in the normal combustion process.