"Packdisks" are collections of different stuff, mostly intros and demos, sampled together on an Amiga disk and equipped with a simple loader menu. Because of their easy usage (no need to run CLI/Workbench) these packages have been quite famous on Amiga back then and likely spreaded and collected. The Packdisks here are released under the flag of Cascade, though some of them might contain a collection of stuff, that is not inevitably made by Cascade members.
All Amiga stuff listed here is archived in the following file types: .zip, .dms, .adz or .adf. All these different file types can be loaded in UAE by simple "drag'n'drop" them into the emulator window (in case this is not possible it's mentioned in the description). Keep in mind, that an Amiga Emulator will need a kickstart rom. More info here.