I will start explaining what Jazz Jackrabbit 2: The Secret Files is by telling the story from the very beginning (others: feel free to correct me if I'm wrong).

1. Jazz Jackrabbit 2 is released. In North America, it is published by GODGames (Gathering of Developers Games). In Europe, it is published by Project 2 Interactive. Later, Epic comes out with a patch to upgrade all shipping versions of Jazz Jackrabbit 2 from version 1.2x to 1.23. That's as far as Jazz Jackrabbit 2 goes.

2. Epic MegaGames decides to make a 'semi-sequel' to Jazz Jackrabbit 2 on a totally different game engine (version 1.24) and call it "Jazz Jackrabbit 2: The Secret Files," in which a third character, Lori, is introduced. This version of Jazz Jackrabbit 2 is not compatible with other versions of Jazz Jackrabbit 2 (its tilesets and levels are not compatible with other versions); a new version of Jazz Creation Station is included with the package. This game was published in Europe by Project 2 Interactive, but, due to financial problems, it was never released in the United States.

There. I've done my best to explain exactly what Jazz Jackrabbit 2: The Secret Files (the short form is "TSF") is. If you REALLY want DETAILED information, check Haze's website (Haze's Hideout). The address: [http://jazz3d.cjb.net]. Hope this helps.