A dump truck is a truck used for transporting materials (usually gravel or some type of soil) 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.
A dump trailer works primarily the same way but is pulled behind a truck as a separate vehicle from the truck. Depending on what type of dump trailer you get the connections to the truck it is being pulled by vary. Most dump trailers can be pulled by a pickup truck equipped with a reese hitch, fifth wheel or ball hitch. When shopping for a dump trailer be sure you look for the one that will work with the type of hitch you already have on your truck or plan on getting one that will work.
I have found the people at Florida Earth Movers are very knowledgeable about these things for the best thing to do would be to call them, as I am sure they can be of great help with such matters.