The term 'fault' comes from the verb "to fail", which itself comes from the popular Latin word for 'to miss'. It was first used in the mining world when the miner could no longer find the layer or vein he was mining.

In geology, a fault refers to a break in the ground with relative displacement, or shifting of the separated parts. The length of faults can vary from a few metres to several hundred kilometres. They can be horizontal (and sometimes generate geological thrust-sheets) or vertical. The two parts separated by the fault are called "walls" and the surfaces torn by the break are called "a rift or "a split". The latter are sometimes polished by friction and show striations that indicate the direction and extent of movement. The extent of the movement is the discharge or displacement.

The fault in front of us is sub-vertical. It separates rocks dating from the Jurassic period. The component or "wall" on the left is dated to the top of the Lower Bajocian period and the one on the right to the base of the Upper Bajocian period. The component or "wall" on the right has therefore subsided in relation to the one on the left. This is called a normal fault. The striations caused by the displacement also reveal a horizontal movement of one component/"wall" in relation to the other. This is known as a split-break or a rift-break.