A strait is a landform connecting two seas or two other large areas of water. The surface water generally flows at the same elevation on both sides and through the strait in either direction. Most commonly it is a channel of water that lies between two land masses. Some straits are not navigable, for example because they are too shallow, or because of an unnavigable reef or archipelago. Straits are also known to be loci for sediment accumulation. Usually, sand-size deposits occur on both the two opposite strait exits, forming subaqueous fans or deltas.
The terms channel, pass, or passage can be synonymous and used interchangeably with strait, although each is sometimes differentiated with varying senses. In Scotland firth or Kyle are also sometimes used as synonyms for strait.
Many straits are economically important. Straits can be important shipping routes and wars have been fought for control of them.
Numerous artificial channels, called canals, have been constructed to connect two bodies of water over land, such as the Suez Canal. Although rivers and canals often provide passage between two large lakes or a lake and a sea, and these seem to suit the formal definition of strait, they are not usually referred to as such. The term strait is typically reserved for much larger, wider features of the marine environment. There are exceptions, with straits being called canals, Pearse Canal, for example.
Straits are the converse of isthmuses. That is, while a strait lies between two land masses and connects two larger bodies of water, an isthmus lies between two bodies of water and connects two larger land masses.
Some straits have the potential to generate significant tidal power using tidal stream turbines. Tides are more predictable than wave power or wind power. The Pentland Firth (a strait) may be capable of generating 10 GW. Cook Strait in New Zealand may be capable of generating 5.6 GW even though the total energy available in the flow is 15 GW.