Rigid parts of the Earth's crust and part of the Earth's upper mantle that move and adjoin each other along zones of seismic activity.
Various-sized areas of the earth's lithosphere that move slowly around the mantle's flowing asthenosphere. Most earthquakes and volcanoes occur around the boundaries of these plates. See lithosphere, plate tectonics.
sections of Earth's rigid crust that move as distinct units on a plastic-like mantle on which they rest. As many as twenty different plates have been identified, but only seven are considered to be major (e.g., Eurasian Plate and the South American Plate).