PlayStation Minis are Sony’s category of downloadable games for the PSP on the PlayStation Network. While Minis are developed primarily for the PSP, some of them are also compatible with the PlayStation 3. Games like The Flying Hamster are part of the Minis line.
The Australian Classification Board board recently put up ratings for three different “Mega Minis” volumes (with no individual games listed) with Sony listed as the publisher. This could mean that Sony are bundling a bunch of Minis together for a retail release.
Sony haven’t said anything about the Mega Minis Volumes officially, so we don’t know when exactly they’ll be released or how much they’ll cost.