MIDI

In simple terms, represents keystrokes of a piano, but it can likely also represent other effects (TODO confirm: bend, vibrato, slides, attack strength)

Can contain multiple parallel tracks as seen from the Wikipedia example: en.wikipedia.org/wiki/File:MIDI_sample.mid

You can see what it contains well with GUI music editor.

MIDI is fun. It is a basic high level representation of most instrumental music, including beats.

To actually listen to MIDI, you need a software synthesizer, which knows what sound to make for each note. One way to specify such instruments is the SoundFont file format.

Convert MIDI to more common standalone formats: