An Armored Personnel Carrier is a Tau'ri military ground vehicle designed to move soldiers (up to 25 in some models) onto the battlefield. Its armor is capable of stopping fragments and rounds from typical infantry rifles. Most have a few machine guns as armaments. If a vehicle has heavier weapons (autocannon, missiles) and armor, its called an Infantry Fighting Vehicle, and is used both for transport and combat.
One (Cadillac Gage Commando, in that particular case) was used by the DEA in their operation to take down the cult leader Seth Fargough. That APC had two guns on the turret and could hold several people and gear. (SG1: "Seth")