In the demoscene, a demopack is a software shell (collection) that combines several works (demo, intro, or graphics) in one interface.
If partypack is just an archive of all files from the festival, then demopack is an independent "product" with a common menu and design.
Main features of demopack: a single interface, thematic integration, music and design, convenience.
Previously, demopacks were a popular distribution method: groups released them as "digital magazines" or progress reports for a specific period. This helped to maintain interest in the group between the release of large megademos.