These are "release groups" or encoders—the individuals/teams responsible for digitizing and uploading the content.
With EGALS Vol 3: Gals Glamourous, Risa Murakami is pushing the boundaries of what's possible in the world of manga. The downgrade to serif is a bold choice, one that pays off in spades. The result is a visually stunning collection that's as much a feast for the eyes as it is a compelling narrative.
The technical differences between (like AVI, MP4, and MKV)