For example:

http://redump.org/discs/system/pc/ only displays PC dumps

http://redump.org/discs/dumper/ajshell1/ only displays my dumps

But some are a bit more hidden.

http://redump.org/discs/errors/null/ only shows discs without an error count

http://redump.org/discs/media/cd only displays discs on CDs.

http://redump.org/discs/region/U/ only shows US region discs.

http://redump.org/discs/language/ seems as though it can be used to filter languages, but I can't get it to work.

But there are a bunch of other search terms that don't seem to be documented anywhere.

For this reason, I think all sorting and filtering terms should be made publicly available somewhere.