Used without modifiers, the word "organ" usually refers to a wind instrument with a keyboard and foot pedals. Playing the instrument activates pipework to produce sounds in a wide array of timbres, called stops, that are arranged in four standard families: flutes, strings, reeds, and principals. This is the instrument that is referred to in the term "church organ" and the version played in The Phantom of the Opera.
The barrel organ is a mechanical instrument that, in some of its incarnations, provides the music in clocks. It is usually a small pipe organ, with a pinned wooden barrel turned by a crank. This both provides air and rotates the barrel and its pins across keys that are engaged and, depending on the placement of the pins, play a tune. The bird organ is a type of barrel organ meant to be used with caged birds to encourage them to sing.
The electronic organ is a pipeless keyboard organ, designed to share many of a pipe instrument’s features. They are able to sustain tones, play chords, and crescendo and decrescendo on sustained tones. Many have a choice of timbres, as do pipe organs. An electric organ is an electronic instrument in which acoustic sounds are combined with pickups or transducers.
A fairground organ is a mechanical instrument that is used on carousels and merry-go-rounds. While the first organs of this type were barrel organs, a mechanism more like a player piano was developed. "Reed organ" is a generic term for instruments with a keyboard and a reed that vibrates freely; these include accordions, concertinas, and harmonicas, also known as mouth organs. A calliope or steam organ produces sound using a pinned cylinder and steam whistles. It was used on river showboats, and appears in the 1951 version of the movie Showboat.
In other contexts, the word organ is both the name for the major, self-contained components of the body, such as the heart, liver, skin, kidneys, brain, as well as for a newspaper or periodical that serves as the voice of an organization.