MIDI file tracks

In music tracks are meaning a musical part of a song. That is a part of the singer or a part of a certain instrument with certain instrument settings. Each one plays its own notes and could also change the instrument settings from time to time.
In MIDI specification this is similar to a MIDI channel. More channels play parallel and each one has its own settings for volume, sound, effects.

In MIDI files tracks and channels have different meaning:
The MIDI file format allows to define one or more parts that all play parallel to the timing that is defined by the first track (conductor track). Each file track plays on one or more channels and each channel uses its own settings that can change during the song.

Depending on MIDI file format the tracks are organized differently.
Format 0: The MIDI file contains only one track and all channels can be used in this track. All commands are sorted by time. This is simplest format for reading since the merging of parallel tracks on the fly is not required.
Format 1: The MIDI file contains first track for conductor (mainly for tempo, tact) and many tracks where each track should play on one channel. All commands inside each track are sorted by time. All tracks are playing parallel. There could be many more tracks than channels. In this case some tracks with share channels and contain only a certain song part e.g. drum solo (logical grouping).
Format 2: The MIDI file contains one or more songs each in a track, each track contains all channels sorted by time (similar to format 0). This format is rarely used and most players do not support this format.

Converting MIDI file format does not change the musical content or sound. The commands are only reorganized inside the MIDI file by merging them to one track or splitting them to more parallel tracks without changing the timing.
During conversion from format 1 to 0 some information might be lost which are not necessary for playing but could be useful for the user (since all commands are merged to a single track): track assignment, track titles. Product GNMIDI 3 converts between format 0 and 1 (GNMIDI 3 Professional also supports batch conversion) and GNMIDFMT 2 converts between format 0, 1, 2 (single and a directory)
Converting might be necessary if a MIDI device does only support one format.