Track 1 is the name used for the game data stored in the GD-ROM's for the Sega Dreamcast. It is presented as an audio file, however many CD-readers and players tend to skip this track as it has over 1 GB and it will present with no data. Then it will play Track 2, which provides warnings of "not playing this disc on a normal cd player". Using special techniques of some sort, you can play track 1 on a regular cd player.
When played, track 1 will play a loud garbled, static-like noise which most cd players can't turn down that will run for approx 112 minutes. Modern and new cd players will either skip to the next track or play the track, with no noise.
However, since such loud and high freq noises are present when played, it might damage cd speakers.