A MIDI (Musical Instrument Digital Interface) controller is a device that sends MIDI data to other MIDI-enabled devices or computers. It allows the user to control and manipulate various parameters of a sound or software synthesizer, such as volume, pan, and modulation. MIDI controllers come in various forms, including keyboards, drum pads, wind controllers, and DJ controllers. They are typically used in music production, performance, and live sound reinforcement to control digital audio workstations, synthesizers, and other MIDI-enabled equipment.