What do we call a crack in the Earth’s crust?

A crack in the Earth's crust is referred to as a fault. Faults are significant geological features that can result from tectonic forces, where blocks of the Earth’s crust have moved relative to each other. This movement can occur horizontally, vertically, or obliquely, and is often associated with earthquakes when stress along the fault line is released.

In geological terms, a fault is distinct from a crevice, which generally refers to a narrow opening or fissure, but not necessarily one that involves movement of crustal blocks like a fault does. Joints, while they are also fractures in the rock, do not involve any displacement of the rock on either side, making them different from faults. Thrusts refer specifically to a type of fault characterized by the movement of rocks along a steep incline, but they still fit within the broader category of faults. Hence, referring to a crack specifically as a fault accurately captures its nature as a point of movement and geological activity.