Tsunamis and tidal waves are definitely not the same thing, although they are often confused with each other.

Tidal waves are caused by the gravitational influences of the sun and the moon, and they actually occur to some extent every day in coastal areas. Under normal circumstances they do no damage—they are simply expected every day as predictable tides.

Tsunamis, on the other hand, are not predictable. They are caused by disturbances in the ocean floor, such as earthquakes. These disturbances displace large quantities of water. A tsunami may not look like anything at all while it is moving through the ocean because its wavelengths are so long. But once the  waves begin to reach the shore the water piles up and floods inland, sometimes with the disastrous results.