A fractured surface in the Earth's crust where a mass of rocks is in motion is called a fault.

Here's a breakdown:

* Fracture: A break or crack in a rock.

* Fault: A fracture in the Earth's crust where there has been movement.

* Motion: The rocks on either side of the fault have moved past each other.

Faults are responsible for earthquakes and can also create mountains and valleys over long periods of time.