MIDI is the Musical Instrument Digital Interface spec that allows computers, synthesizers, samplers etc. to communicate digitally. Cubase also records and edits MIDI information, including musical performances on keyboards, fretted instruments like guitars and drum sets. So you could record a MIDI performance on a keyboard, then change the notes, tempo, key, velocity of keystrokes and even sounds that are being triggered.

The MIDI interface connects a MIDI device with the computer.