It is difficult to explain this diverse format with just a few words. In general a MIDI (Musical Instrument Digital Interface) is a transmission protocol for commanding synthesizers. The commands are for example: "Note on", "Note off", Touch, tone pitch, instrument etc.
Further information on MIDIfiles, their origin and usage can be found here.
In our product groups there are 3 different names for MIDIfiles, which relate to the available formats: