To purposely drain your teammate's health so they will be killed by an opponent more easily.
Most often associated with a team slayer game type in Halo 3.
"Dude, I just got the most epic tenderize on Skarth with this power drain!"
Player 1: "WTF dude, I died so easily."
Player 2: "lol I was tenderizing you"
"lol stop tenderizing me so we can win"