A swimming pool, swimming bath, wading pool, or paddling pool is a structure designed to hold water to enable swimming or other leisure activities. Pools can be built into the ground (in-ground pools) or built above ground (as a freestanding construction or as part of a building or other larger structure), and are also a common feature aboard ocean-liners and cruise ships. In-ground pools are most commonly constructed from materials such as concrete, natural stone, metal, plastic or fiberglass, and can be of a custom size and shape or built to a standardized size, the largest of which is the Olympic-size swimming pool.
Many health clubs, fitness centers and private clubs, such as the YMCA, have pools used mostly for exercise or recreation. Many towns and cities provide public pools.