A fracture zone is a linear oceanic feature--often hundreds, even thousands of kilometers long--resulting from the action of offset mid-ocean ridge

Mid-ocean ridge

A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...

 axis segments. They are a consequence of plate tectonics

Plate tectonics

Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

. Lithospheric plates on either side of an active transform fault

Transform fault

A transform fault or transform boundary, also known as conservative plate boundary since these faults neither create nor destroy lithosphere, is a type of fault whose relative motion is predominantly horizontal in either sinistral or dextral direction. Furthermore, transform faults end abruptly...

 move in opposite directions; here, strike-slip activity occurs. Fracture zones extend past the transform faults, away from the ridge axis; seismically inactive (because both plate segments are moving in the same direction), they display evidence of past transform fault activity, primarily in the different ages of the crust on opposite sides of the zone.

In actual usage, many transform faults aligned with fracture zones are often loosely referred to as "fracture zones" although technically, they are not.