Question about Midnight's Blade

Hey guys,

I have a quick question about Midnight's Blade and "once per turn" abilities in general, and I'd love to get some official feedback.

My question is this: What does "once per turn" truly mean? Does it mean once per player turn (the 'player' here being the person who activated the ability [Midnight's Blade for instance] in the first place)? Or does it mean once per round, or even once per every individual PC and NPC combatant's turn in the round? I was told it was the latter interpretation, but I wanted to be sure as that drastically changes the way I'd originally thought the ability worked.

Thanks for your time!