Final answer:
Uniformitarianism is not another term for the theory of massive crustal deformation. Uniformitarianism is the theory that the same natural laws and processes have always operated in the universe, while the theory of massive crustal deformation refers to plate tectonics, which explains the movement of Earth's crust.
Step-by-step explanation:
Uniformitarianism is the theory that the same natural laws and processes that operate in our present-day scientific observations have always operated in the universe in the past and apply everywhere in the universe. It is sometimes referenced as 'The present is the key to the past'. This theory is different from the theory of massive crustal deformation, which is the concept of plate tectonics. Plate tectonics explains how slow motions within the mantle of Earth move large segments of the crust, resulting in the drifting of continents and the formation of mountains and other geological features.