A 4x4 truck for sale is a four-wheel-drive pickup truck being offered for sale, usually by its owner or a dealership. The denotation "4x4" means that the vehicle has four wheels with power provided to each wheel.
When using numerical shorthand, the first number refers to the number of wheels and the second number refers to how many of them are powered. For example, a 4x2 would be a four-wheeled vehicle with only front-wheel drive. It can be useful shorthand for all-terrain vehicles, since some have more than four wheels. There are some triple-axle trucks that have six wheels but are still four-wheel-drive because only the back two axles are powered, for example.
"Truck" usually refers to pickup trucks when talking about 4x4s. These are vehicles with an enclosed cab and an open bed, although products such as camper shells can be added to enclose the bed. This is in contrast to other types of 4x4 vehicles, such as Jeeps. However, the term may be used colloquially to describe a variety of vehicle styles.
Although 4x4 trucks are popular for off-road use or exploring rough terrain, they can also be used for other purposes. Many people prefer them for towing livestock trailers, campers and other heavy loads, especially if they may need to haul in inclement weather or cross dirt roads and areas that require a high clearance.