Apparently, it's the EVAP charcoal canister. You can technically remove it but having it on doesn't hurt performance or anything. The purpose of it is to trap gas vapor to reduce emissions, and to trap the gas from escaping, recycling some of it on engine start up. As a result, it also reduces the smell of gasoline coming from your car when it's not running.
If you do end up removing it, just remember not to cap the vapor line that usually goes into the canister. There are some that did that and had gas being pushed up into the intake of the engine after they had the car turned off.