What type of plate boundary forms when two tectonic plates slide horizontally past each other?

A transform boundary forms when two tectonic plates slide horizontally past each other.

Transform motion is mainly sideways, so it is also called strike-slip motion. The plates may move in opposite directions along a fault, building stress when friction locks the boundary. Sudden release of that stress produces earthquakes.

Transform boundaries differ from divergent boundaries, where plates move apart, and convergent boundaries, where plates move together. They generally do not create or destroy large amounts of crust, although local deformation can be complex.

The San Andreas Fault is a famous continental transform boundary between the Pacific and North American plates. Many oceanic transform faults offset segments of mid-ocean ridges. Transform faults can generate damaging shallow earthquakes because rupture occurs relatively close to the surface and may extend beneath populated areas.