Trucks by size:

Light trucks (weighing no more than 13,000 lb)
Medium trucks (weighing between 13,000 and 33,000 lb)
Heavy trucks are the largest trucks, mostly used for long-haul purposes, often in semi-trailer or B-double configuration.

Dump Truck:

A 'Dump Truck' is a truck used for transporting loose materials such as sand, gravel, or dirt for construction. A typical dump truck is equipped with a hydraulically operated open-box bed hinged at the rear, the front of which can be lifted up to allow the contents to be deposited on the ground behind the truck at the site of delivery.

Tow Truck:

A 'Tow Truck', also called a Wrecker, a breakdown truck is a truck used to tow diabled vehicles to another location (to a repair shop or garage) when it breaks-down or had a collision, or to impound illegally parked vehicles.