Definition of fault

i. A fracture or a fracture zone in crustal rocks along which there has been displacement of the two sides relative to one another parallel to the fracture. The displacement may be a few inches or many miles long.

ii. A break in the continuity of a body of rock. It is accompanied by a movement on one side of the break or the other so that what were once parts of one continuous rock stratum or vein are now separated. The amount of displacement of the parts may range from a few inches to thousands of feet. Various descriptive names have been given to different kinds of faults, including closed fault; dip fault; dip-slip fault; distributive fault; flaw fault; gravity fault; heave fault; hinge fault; horizontal fault; longitudinal fault; normal fault; oblique fault; oblique slip fault; open fault; overthrust fault; parallel displacement fault; pivotal fault; reverse fault; rotary fault; step fault; strike fault; strike-slip fault; thrust fault; transcurrent fault; translatory fault; underthrust; vertical fault; want.

iii. In coal mining, a sudden thinning or disappearance of a coal seam. Also known as a want or pinchout.

Ref: Kentucky