patch: a small program that goes into the image file (copy of the CD on you hard drive) and makes a few small changes to eliminate some things.

selector: allows you to choose what country code you are in. games that are released in japan are not supposed to be able to be played in america, but a selector will give you the option to say what country you are in, so you will be able to play a japanese import on your american playstation (or vice versa).

protection fix: sometimes people put this down and it means the same thing as the "selector," but if you see both a "protection fix" and a "selector" listed for the same patch, that probably means that it eliminates the mod-chip protection that has been written into the game as well. (look at the first legend of dragoon @ http://megagames.com/console/psx_patches_l.htm)

hope that helps