What is the difference between a tsunami and a tidal wave?

In December 2004, when a tsunami killed more than 200,000 people in 11 countries around the Indian Ocean, the United States was reminded of its own tsunami risks. In fact, devastating tsunamis have struck North America before and are sure to strike again. Especially vulnerable are the five Pacific States–Hawaii, Alaska, Washington, Oregon, and California–and the U.S. Caribbean islands…