A dex Ps3 is a ps3 on a "Dex CFW". Dex means its debugged, which means you can debug games in real time, among other things. Mainly it allows you to poke offsets while playing a game, letting you edit the eboot in real time... Kinda where the Term "Real Time Editing" came from.
The following user thanked BaSs_HaXoR for this useful post: