noun
Refers to a narrow waterway connecting two larger bodies of water. Often appears in place names such as 瀬戸内海 (Seto Inland Sea).
この瀬戸は潮の流れが速い。
The current in this strait is fast.
瀬戸大橋は本州と四国を結んでいる。
The Seto Ohashi Bridge connects Honshu and Shikoku.
海峡 is a more formal or technical term for a strait or channel, while 瀬戸 is often used in place names and has a slightly more traditional or local feel.
The word is of native Japanese origin. The kanji 瀬 (rapids, shallows) and 戸 (gate, door) together suggest a narrow water passage, but the exact historical derivation is uncertain.