Real Dictionary

plate tectonics
uncountable noun: Plate tectonics is the study of the way that large pieces of the Earth's surface move slowly around.

plate tectonics in American English
the theory that the earth's surface consists of plates, or large crustal slabs, whose constant motion explains continental drift, mountain building, etc.
noun: a theory of global tectonics in which the lithosphere is divided into a number of crustal plates, each of which moves on the plastic asthenosphere more or less independently to collide with, slide under, or move past adjacent plates

plate tectonics in British English
noun: 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 bou