The movement of the Earth's rock plates is primarily driven by the processes associated with plate tectonics. This includes:
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Convection Currents in the Mantle: The heat from the Earth's core causes convection currents in the mantle, which in turn causes the tectonic plates on the Earth's surface to move.
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Slab Pull: As denser oceanic plates subduct (sink) into the mantle at convergent boundaries, they pull the rest of the plate along with them.
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Ridge Push: At divergent boundaries, as magma rises to create new crust, it pushes the tectonic plates apart.
These mechanisms, along with the Earth's internal heat, are responsible for the continual movement of Earth's plates. If you were looking for one overarching term, "convection currents in the mantle" is often considered the primary driver of plate movements.