A Swivel is a mechanical device used on a drilling rig

Drilling rig (petroleum)

This article lists the main components of a petroleum onshore drilling rig.Offshore drilling rigs have similar elements, but are configured with a number of different drilling systems to suit drilling in the marine environment....

 that hangs directly under the traveling block

Traveling block

A traveling block is the freely moving section of a block and tackle that contains a set of pulleys or sheaves through which the drill line is threaded or and is opposite the crown block ....

 and directly above the kelly drive

Kelly drive

A kelly drive refers to a type of well drilling device on an oil drilling rig that employs a section of pipe with a polygonal or splined outer surface, which passes through the matching polygonal or splined kelly bushing and rotary table...

, that provides the ability for the kelly (and subsequently the drill string

Drill string

A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid and torque to the drill bit. The term is loosely applied as the assembled collection of the drill pipe, drill collars, tools and drill bit...

) to rotate while allowing the traveling block to remain in a stationary rotational position (yet allow vertical movement up and down the derrick) while simultaneously allowing the introduction of drilling fluid

Drilling fluid

In geotechnical engineering, drilling fluid is a fluid used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells. Liquid drilling fluid...

 into the drill string.

See Drilling rig (petroleum)

Drilling rig (petroleum)

This article lists the main components of a petroleum onshore drilling rig.Offshore drilling rigs have similar elements, but are configured with a number of different drilling systems to suit drilling in the marine environment....

for a diagram of a drilling rig.