The term for the movement of tectonic plates is plate tectonics. This scientific theory explains how the Earth's lithosphere (the rigid outer layer) is divided into several large and small plates that float on the semi-fluid asthenosphere beneath them. These tectonic plates constantly move due to convection currents in the mantle, leading to geological activity such as earthquakes, volcanic eruptions, and the creation of mountains. Plate tectonics is fundamental to understanding the Earth's geological history, the formation of continents, and the dynamic nature of the planet's surface.