Commercial truck classification is generally determined based on the vehicle's gross vehicle weight rating (GVWR). For example, in USA classes range from 1-8 which groups Class 1-3 as "Light Duty", 4-6 as "Medium Duty", and 7-8 as "Heavy Duty". Below are most the common commercial trucks we often see.
Refrigerated Trucks/reefer loads - these trucks use a refrigeration unit in the cargo area to protect freight that must be kept at or below specific temperatures sometimes frozen or even below frozen.
Flatbed Trucks/flatbed loads - are trucks that have flat, level body with no sides or roof. This allow for quick and easy loading and unloading of oversize loads such as airplanes, scaffolding for construction, and other freight that require more space than is available inside of a trailer.
Tank trucks/tankers - used mostly to haul liquids like gasoline you use everyday or milk, dry bulk cargo like sugar and cement, or gasses on roads which may be highly explosive. Tank trucks tend to be large and may be designed for single or multiple loads (internal divisions in the tank).
Auto-carrier trucks - are the special trailers loaded up with all types of vehicles. Trucks that transport cars from a port or an auction to your local lots.