Often used as a climbing term the phrase "Belay on" can also be used in regular conversation to let someone know they have YOUR permission to proceed on with whatever they are doing or about to do.
Roommate 1: "Dude I'm gonna go drop a duece, ok?
Roommate 2:"Belay on, Bro."
Roommate 1: "Hey man I think I'll take out the trash tonight."
Roommate 2: "Belay on."