(n.) The state of being so high that you can't get off of your couch; being unable to move/speak/stand.
Joe: "You awake, Pat?"
Joe: "Yeah, he's couch locked."
Being so stoned that you can do nothing but sit on the couch laughing at stoner movies.
"Hey man, we're going to the store to get some munchies, you coming?"
"Ha, don't even try it, man, he's got couch lock."