海啸是一种具有强大破坏力的海浪。当地震发生于海底，因震波的动力而引起海水剧烈的起伏，形成强大的波浪，向前推进，将沿海地带一一淹没的灾害，称之为海啸。

海啸在许多西方语言中称为“tsunami”，词源自日语“津波”，即「港边的波浪」（「津」即「港」）。这也显示出了日本是一个经常遭受海啸袭击的国家。汉字又称海溢。台语称海涨（hái-tiòng）。“tsunami”一词，在1963年的国际科学会议上正式列入国际术语。目前，人类对地震、火山、海啸等突如其来的灾变，只能透过观察、预测来预防或减少它们所造成的损失，但还不能阻止它们的发生。

A tsunami (plural: tsunamis or tsunami; from Japanese:津波, lit. "harbor wave"; English pronunciation: /tsuːˈnɑːmi/) , also known as a seismic sea wave, is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami. Unlike normal ocean waves which are generated by wind or tides which are generated by the gravitational pull of the Moon and Sun, a tsunami is generated by the displacement of water.