MIDI is a specific type of music file, not related to chiptunes in any way. It is actually a communication protocol for musical information, so for example you can send MIDI data to an external synthesizer and it will play the notes using its own sounds. But your computer can also play MIDI songs, it will sound a little different based on what system is playing it but the file sizes are incredibly small compared to real audio.
I know what a MIDI file is. THE THING IS, sometimes the Devs will mistake a 16 bit song with the sound of a MIDI file which is very similar to an extent, I was asking for clarification in that regard. So much so that it's a very unusual request for a Dev to want MIDI files in his game instead of the classic 8 Bit / 16 Bit / 32 Bit NES / SNES / PS1 era.