A box truck, as the name suggests, holds a box-like cargo area which is separate to the cab and housed on a frame. Whereas a cargo truck is a one-piece vehicle where the cab and cargo area are attached and accessible via one another.
Some box trucks for sale may have a grafted cargo area which is attached to the cab, allowing for access to the cargo area. However in most cases the cab and the cargo area are completely separate.
The cargo area of the truck is usually secured by a pull-up roller door, as per a garage door.
Box trucks are used for the storage and delivery or larger items such as furniture and as such box trucks are commonly used by haulage and removal companies due to their capacity to hold such weight.