tsunami (lang-ja?? IPA-jats?nami, lit. harbor wave; IPA-ensu??n??mi or IPA-entsu??n??mi) or tidal wave is a series of water waves (called a tsunami wave train) caused by the displacement of a large volume of a body of water, such as an ocean or a large lake (Tsunami hazard in lakes). Tsunamis are a frequent occurrence in Japan; approximately 195 events have been recorded. Due to the immense volumes of water and energy involved, tsunamis can devastate coastal regions. Casualties can be high because the waves move faster than humans can run.

Earthquakes, volcanic eruptions and other underwater explosions (detonations of nuclear devices at sea), landslides and other mass movements (mass wasting), bolide impacts (impact event), and other disturbances above or below water all have the potential to generate a tsunami.

The Greek (Ancient Greece) historian Thucydides was the first to relate tsunami to submarine earthquakes, but understanding of tsunamis nature remained slim until the 20th century and is the subject of ongoing research. Many early geological, geographical, and oceanographic texts refer to tsunamis as "seismic sea waves."

Some meteorological conditions, such as deep depressions (depression (meteorology)) that cause tropical cyclones, can generate a storm surge, called a meteotsunami, which can raise tides several metres above normal levels. The displacement comes from low atmospheric pressure within the centre of the depression. As these storm surges reach shore, they may resemble (though are not) tsunamis, inundating vast areas of land. Such a storm surge inundated Burma (Myanmar) in May 2008.