The crust (upper part) of the earth has been formed out of seven major and some minor plates. These are called tectonic plates.
A Tectonic plate (also called lithospheric plate) is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. Plate size can vary greatly, from a few hundred to thousands of kilometers across; the Pacific and Antarctic Plates are among the largest. Plate thickness also varies greatly, ranging from less than 15km for young oceanic lithosphere to about 200km or more for ancient continental lithosphere.