Electric organ in the context of "Theatre organ"

Jazz fusion (also known as jazz rock, jazz-rock fusion, or simply fusion) is a popular music genre that developed in the late 1960s when musicians combined jazz harmony and improvisation with rock music, funk, and rhythm and blues. Electric guitars and basses, amplifiers, and keyboard instruments (including electric pianos and organs) that were popular in rock began to be used by jazz musicians, particularly those who had grown up listening to rock and roll.

Jazz fusion arrangements vary in complexity. Some employ groove-based vamps fixed to a single key or a single chord with a simple, repeated melody. Others use elaborate chord progressions, unconventional time signatures, or melodies with counter-melodies, in a similar fashion to progressive rock. These arrangements, whether simple or complex, typically include improvised sections that can vary in length, much like in other forms of jazz.

The Hammond organ is an electric organ invented by Laurens Hammond and John M. Hanert, first manufactured in 1935. Multiple models have been produced, most of which use sliding drawbars to vary sounds. Until 1975, sound was created from rotating a metal tonewheel near an electromagnetic pickup, and amplifying the electric signal into a speaker cabinet. The organ is commonly used with the Leslie speaker.

Around two million Hammond organs have been manufactured. The organ was originally marketed by the Hammond Organ Company to churches as a lower-cost alternative to the wind-driven pipe organ, or instead of a piano. It quickly became popular with professional jazz musicians in organ trios—small groups centered on the Hammond organ. Jazz club owners found that organ trios were cheaper than hiring a big band. Jimmy Smith's use of the Hammond B-3, with its additional harmonic percussion feature, inspired a generation of organ players, and its use became more widespread in the 1960s and 1970s in genres such as rhythm and blues, rock (especially progressive rock), and reggae.

The word "manual" is used instead of the word "keyboard" when referring to any hand-operated keyboard on a keyboard instrument that has a pedalboard (a keyboard on which notes are played with the feet), such as an organ; or when referring to one of the keyboards on an instrument that has more than one hand-operated keyboard, such as a two- or three-manual harpsichord. (On instruments that have neither a pedalboard nor more than one hand-operated keyboard, the word "manual" is not a synonym for "keyboard".)

Music written to be played only on the manuals (and not using the pedals) can be designated by the word manualiter (first attested in 1511, but particularly common in the 17th and 18th centuries).

Bass pedals are an electronic musical instrument with a foot-operated pedal keyboard with a range of one or more octaves. The earliest bass pedals from the 1970s consisted of a pedalboard and analog synthesizer tone generation circuitry packaged together as a unit. The bass pedals are plugged into a bass amplifier or PA system so that their sound can be heard. Since the 1990s, bass pedals are usually MIDI controllers, which have to be connected to a MIDI-compatible computer, electronic synthesizer keyboard, or synth module to produce musical tones. Some 2010s-era bass pedals have both an onboard synth module and a MIDI output.

Bass pedals serve the same function as the pedalboard on a pipe organ or an electric organ, and usually produce sounds in the bass range, which, in organ terminology is the 16′ stop. Some bass pedals have an 8′ stop (an octave higher) which can be used by itself or combined with the 16' stop. Bass pedals are used by keyboard players as an adjunct to their full-range manual keyboards (the keyboards played with the hands), by performers of other instruments (e.g., electric bass or electric guitar), or by themselves. Bass pedal units usually have a smaller range (13 notes) than a church pipe organ's pedal keyboard (32 notes for an American Guild of Organists standard pedalboard). Bass pedals with larger ranges are less common, but do exist, such as 17 notes (C to E), 20 notes (C to G), and 25 notes (C to C two octaves higher). As well, bass pedals usually have shorter pedals than those on a church pipe organ's pedalboard.