A water slide is a type of slide or tube designed for warm-weather or indoor recreational use, typically with water pumped to its top and allowed to flow down its surface, although some may simply be wet. A person is able to sit directly on the slide, or on a raft or tube designed to be used with the slide, and slide to the bottom via gravity. The water reduces friction so sliders travel down the slide very quickly.

Water slides typically run into a swimming pool (often called a plunge pool) at the end. Some, however, have long, flat, straight sections at the bottom with a few inches of standing water, frictional material, or rollers attached to the slide designed to slow the slider and allow them to safely exit the slide.

Water slides are popular at water parks and may form alternatives to those who don't like such intense rides at other amusement parks. If these empty into a pool, the pool is usually designed only to catch sliders who must exit the pool immediately after coming to a stop, to prevent sliders entering the pool at high speed from striking other swimmers. These Plunge pools are usually quickly cleared by other swimmers to avoid injury. Smaller water slides may be found at actual swimming pools in water parks, private locations and community recreation centers where larger "thrill" slides are absent.