sequencer
1. In computer music, either a computer program or hardware that allows a composer to arrange a sequence or sequences of musical notes. These may then be replayed as continuous loops or on receipt of some trigger event. Often the anchor note for the sequence may be input by means of a conventional MIDI keyboard. Early sequencers were monophonic hardware solutions, often custom-built. Many modern computer programs for music composition can be viewed as sequencers, but it is the ability to loop, be triggered, and to alter the anchor note that gives the composer the ability to use sequencer technology in live performance.

2. A logic circuit that produces outputs that are intended to provide coordination stimuli for other logic circuits. The exact timing and sequence of these control outputs is dependent on the sequencer circuitry and may depend on a set of input control signals provided by external devices.

se·quenc·er / ˈsēkwənsər/ • n. 1. a programmable electronic device for storing sequences of musical notes, chords, or rhythms and transmitting them when required to an electronic musical instrument.2. Biochem. an apparatus for determining the sequence of amino acids or other monomers in a biological polymer.

sequencer. Elec. device enabling a succession of several sounds (together with modifications in each) to be pre-set.