Deformation refers to the alteration of the shape or volume of a rock body in response to stress, including processes like folding, faulting, and fracturing. Deformation is a key concept in structural geology and tectonics, helping to explain the formation of mountains, earthquakes, and other geological structures.
Reference: Twiss, R. J., & Moores, E. M. (2007). “Structural Geology.” W. H. Freeman.