An Armoured Personnel Carrier intended to deliver its payload of a couple of squads of squaddies to the fight BUT not intended to hang around to support them.
Examples of this beast would be a M113.
or an FV432
Armament would be unlikely to exceed a 7.62mm Machine gun. Anything larger will likely make the vehicle into an Infantry Fighting Vehicle (IFV) or a Mechanized Infantry Combat Vehicle (MICV).