A strait is a naturally formed, narrow, typically navigational way by water. As usual it joins two larger bodies of water. Most commonly it is a channel of water that flows between two parts of land masses. Some straits are not navigable because they are too shoal or because of a navigational bed which has a lot of reef or archipelago. The terms channel, pass or passage, can be synonymous and used interchangeably with strait. But each is very often differentiated with varying senses.

Many straits are important for economic. Straits can be significant for shipping routes. In wars time it has been fought for control of them.

A lot of non-natural channels, called canals, have been constructed to connect two bodies of water over land. The Suez Canal is excellent example of it. Although rivers and canals often provide pass between two large lakes or a lake and a sea. These passes seem to suit the formal definition of strait; they are not usually mention in this meaning. The term strait is typically reserved for much larger, wider features of the water environment. However, sometimes there are exceptions, with straits being called canals. For example, Pearse Canal.

Straits are the opposite of isthmuses because isthmus flows between two bodies of water and connects two larger land masses.

Some straits have the potential and power for generating significant tidal power by using tidal stream turbines. Tides are more predictable than wave power or wind power.

Straits are used for international navigation through the territorial sea between one part of the high seas or an exclusive economic zone and another part of the high seas or an exclusive economic zone which are supposed to be subject to the legal regime of transit passage.