The term "repack" refers to a heavily compressed version of a video game, designed to reduce massive download sizes while keeping the core gameplay intact. The repack by the legendary scene releaser, Mr DJ, has been a staple in the archiving community for several reasons:
Custom repacks like the one you mentioned often include the base game plus additional content, such as mods, fixes for bugs not addressed by the official patches, or even extra game content. These are usually created by fans or modding communities.