What type of fault involves rocks on either side moving past each other with little vertical motion?

A strike-slip fault is characterized by the lateral movement of the rocks on either side of the fault line, with minimal vertical displacement. This type of fault occurs primarily due to horizontal shear stress, leading to the blocks of crust slipping past one another along a nearly vertical fracture. The motion along strike-slip faults can be right-lateral or left-lateral, depending on the direction of movement observed from a reference point on one side of the fault.

In contrast, normal faults and reverse faults involve significant vertical motion. Normal faults occur where the crust is being pulled apart, allowing one block to move downwards relative to another. Reverse faults, on the other hand, are formed by compressional forces pushing two blocks together, resulting in one block being thrust upward. Thrust faults are similar to reverse faults, but they typically have a shallower dip, also resulting in vertical displacement. Therefore, the defining feature of strike-slip faults lies in their lateral motion, making it the correct answer to the question.