A conventional truck is a type of truck with its engine in front of the driver (much like in a typical car), as opposed to underneath with no nose like in a cab over

Cab over

Cab-over, also known as COE , cab forward, or forward control, is a body style of truck or van that has a vertical front or "flat face", with the cab of the truck sitting above the front axle...

. This model is the most popular for American truckers. The design gives the driver more leg room and a smoother ride. These models of semi-trucks hold their re-sale value much better than the cab-over engine models.