A swimming-pool is “an artificially enclosed body of water”. It is a wide water container, usually built in the ground. Swimming pools are water pools for people to swim or to indulge themselves in many water-based and funny activities.
Basically there are two types of pools: private pools and public pools. Standards size and shape for a pool vary upon many factors: the intended use (for recreation or competition, for relaxing or for children), the access requirements (public or private, free or not)...

For swimming-related sports, such as swimming, synchronized swimming, water polo (...) pools are rectangular-shaped. The longest pool, used for competitions, is the Olympic pool: a 50 meters long and 25 meters wide pool. Most frequently, public pools opened for members of a pool's club to train measure 25 meters in length.
Pools, when they are deep enough, may also be used for diving.
Most public pools are part of a huge recreational complex, featuring a ticket desk, several locker rooms, showers (showering before entering the pool is usually compulsory, for the public to get rid of their little bacteria...), children pools (shallow for preventing drownings), steam baths, sauna, hot tubes, Jacuzzis, water slides...

Private pools encompass two types of pools: the inflatable pools, and the others!
Inflatable pools are usually for children to have fun in the water when the heat is oppressive. They don't require to be filled up with a great volume of water, yet you can't really swim in them and they often burst for no reasons.
The “others” are copied on public pools, except that most of them are shaped pretty weirdly: kidney-shaped pools, heart shaped pool...pool designers don't run out of ideas to attract the customers...

If, as a child, you went to public pools with your class, I'd bet you remember the smell of your hair after your swimming lesson, the lifeguard blowing his whistle to warn you against the danger of running alongside the pool, the sensation of your hair pulled off when you took your bathing cap off, the speedos and other dressing codes...

yet, many holiday resorts and spas would surely reconcile you with swimming pools: the largest pool in the world is San Alfonso Del Mar Seawater pool, in Chile.
It is, and I quote: “1,013 m (3,324 ft) long and has an area of 8 ha (20 acres)”.