A fault is a fracture in the Earth's crust where there has been movement. The movement can be horizontal, vertical, or a combination of both. The amount of displacement along a fault can vary from just a few millimeters to hundreds of kilometers.

Here are some additional terms related to faults:

* Footwall: The block of rock below the fault.

* Hanging Wall: The block of rock above the fault.

* Fault Plane: The surface of the fracture.

* Fault Scarp: A cliff or step in the landscape that is formed by the movement along a fault.

Let me know if you have any other questions!