Organ stop

The choir division of the organ at St. Raphael's Cathedral, Dubuque, Iowa. Shown here are several ranks of pipes, each of which would be controlled from one of the stops on the console.

An organ stop is a component of a pipe organ that admits pressurized air (known as wind) to a set of organ pipes. Its name comes from the fact that stops can be used selectively by the organist; each can be "on" (admitting the passage of air to certain pipes), or "off" (stopping the passage of air to certain pipes).

The term can also refer to the control that operates this mechanism, commonly called a stop tab, stop knob, or drawknob. On electric or electronic organs that imitate a pipe organ, the same terms are often used, with the exception of the Hammond organ and clonewheel organs, which use the term "drawbar".

The term is also sometimes used as a synonym for register, referring to rank(s) of pipes controlled by a single stop. Registration is the art of combining stops to produce a certain sound. The phrase "pull out all the stops", which once only meant to engage all of the voices on the organ, has entered general usage, for deploying all available means to pursue a goal.