What do we call the movement of Earth’s plates?

The movement of Earth’s plates is referred to as plate tectonics. This term encompasses the theory that explains how the Earth's lithosphere is divided into several large plates that glide over the more fluid asthenosphere beneath. These tectonic plates continuously move, albeit very slowly, and their interactions lead to various geological events and formations, such as earthquakes, volcanic activity, and the creation of mountain ranges.

While continental drift specifically describes the movement of continents over geological time, it is a concept within the broader theory of plate tectonics. Seafloor spreading explains the process by which new oceanic crust is generated at mid-ocean ridges, an aspect of plate tectonics, but does not encompass the full range of plate movement. Volcanism refers to the eruption of magma from within the Earth, which can be a result of the movement of tectonic plates but does not describe the movement itself. Thus, the term that best captures the overall phenomenon of how Earth's plates are moving is indeed plate tectonics.