From Dictionary.com:

movement resulting from or causing deformation of the earth's crust. crustalmovement. geology - a science that deals with the history of the earth as recorded in rocks. motion,movement - a natural event that involves a change in the position or location of something.

The lithosphere of the earth is divided into a small number of plates which float on and travel independently over the mantle and much of the earth's seismic activity occurs at the boundaries of these plates.

From the deepest ocean trench to the tallest mountain, plate tectonics explains the features and movement of Earth's surface in the present and the past. Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. Plates at our planet's surface move because of the intense heat in the Earth's core that causes molten rock in the mantle layer to move. It moves in a pattern called a convection cell that forms when warm material rises, cools, and eventually sink down. As the cooled material sinks down, it is warmed and rises again.

Try to learn about the TYPES of tectonic plate movements :-)