Plate tectonics is the way that large pieces of the Earth's surface move slowly around.
[technical]
plate tectonics in British English
noun
(functioning as singular) geology
the study of the structure of the earth's crust and mantle with reference to the theory that the earth's lithosphere is divided into large rigid blocks (plates) that are floating on semifluid rock and are thus able to interact with each other at their boundaries, and to the associated theories of continental drift and seafloor spreading
plate tectonics in American English
Geology
the theory that the earth's surface consists of plates, or large crustal slabs, whose constant motion explains continental drift, mountain building, etc.