A swimming pool is a large container filled with water where people can swim, play, or cool off. Some pools are built into the ground with concrete or tile, while others are temporary structures that can be set up and taken down. Public pools might be Olympic-sized rectangles for serious swimming and competitions, while backyard pools come in all shapes and sizes.

Pools need constant care to stay clean and safe. Filters remove dirt and debris, while chemicals like chlorine kill bacteria and help keep the water clear. That distinctive pool smell you notice? It's actually chlorine reacting with tiny bits of dirt and sweat.

Swimming pools have an interesting history. The ancient Greeks and Romans built elaborate public baths and pools thousands of years ago. Modern swimming pools became popular in the early 1900s, when cities built public pools so more people could learn to swim and stay cool in summer. Today, competitive swimmers train in pools with lane lines and starting blocks, while neighborhood pools are gathering places where kids play Marco Polo and practice diving.

The term can also describe a small, temporary collection of water, like a pool of rainwater in a parking lot, though this meaning is less common than the swimming kind.