Originally Posted by Twoxentrix
I believe that one is mounted so you can lift the bed platform up for access, then pull the leg out to support it in the open position - similar concept that keeps your front hood up so you don't have to hold it.
Yep, it's a prop rod. Mostly I just wanted to say prop rod, because that name cracks me up.
However, every person I know (including me) has always called it that. Perhaps it's a southern thing.