Tsunami is a Japanese word meaning "harbor wave," a rather benign term for such a disastrous natural event.
The Indian Ocean tsunami of 26 December 2004 riveted world attention on this phenomenon. Numerous tourist videos showed rising waters sweeping away people and structures. News reports showed the tragic human aftermath. Satellites captured the westward movement of wave trains across the Indian Ocean that took several hours to travel from Indonesia to the east coast of Africa.
A tsunami is a "packet" of energy radiating outward from its point of origin. It is triggered by a powerful underwater event that imparts a massive pulse of energy to the sea.