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.
Finding the right dump truck for the type of work you have in mind can be a mind boggling experience. Most people prefer the tandem axle kind thinking that a single axle will not hold up for heavier loads. This may be true for hauling heavy materials like rock and sand but for general trash hauling a single axle dumptruck will work just fine. I have even seen single axle dump trucks with lighter aluminum dump trailers hauling sand with no problem.
Also why get a huge dump truck when a small one will do...if it's a one time job just for yourself you can get by with a small one. If you are in the business of hauling for others then you need something that can haul as much as possible and that can handle as much weight as possible...this way you aren't limited to what you can haul and there will be more opportunities for work. You can find a list of used dump trucks here.