The term for the shifting of tectonic plates along fault lines is plate tectonics. This process involves the movement of large slabs of the Earth's crust, known as tectonic plates, which float on the semi-fluid mantle beneath. The interaction between these plates can cause earthquakes, volcanic eruptions, and the formation of mountains. The boundaries where these plates collide, pull apart, or slide past each other are known as fault lines, making plate tectonics a fundamental aspect of Earth's geological dynamics.