Note Tracks
From Audacity Manual
Note Tracks display data from MIDI files - these can be imported with the command. Note Tracks cannot currently be played, but can be cut-and-paste edited, then exported using the command.
Despite the currently limited functionality, Note Tracks can be useful to visually compare a given MIDI file with a sampled audio file (such as WAV) of the same music.
When exporting so as to overwrite an existing GRO, MID or MIDI file, the original file is renamed with ".bak" suffix, for example "keyboards.mid.bak".