MIDI is mainly some music digital control signals, which can send all kinds of instructions needed by music to all MIDI devices through music sequencer to complete music performance. It can also be used to control MIDI devices other than music, such as the lighting console.
About the general situation of Midi, you can use Baidu to search for Midi Baidu Encyclopedia:
In addition, it needs to be corrected that MIDI protocol can refer to sending signals through USB, but in most cases, the recognized MIDI interface is a five-core interface made by Din in Germany. Some people say that MIDI-Din is not a German standard, which is wrong.
Germany has a five-core interface made of Din (at first, it only transmits audio signals, and the shielded wire is grounded). Later, MIDI protocol adopts a five-core interface made of Din.
If you are a music major, you should spend some time learning about MIDI.