[mason55]

Yes basically it's a situation that is +EV. For example (in limit) if there's 10BB in the pot after the turn and you're drawing to a flush, you call your lone opponents bet. The odds of hitting are 4:1 and the odds the the pot is offering is 11:1. In this case you're getting an overlay of 8 bets, a very favorable situation. The idea is that you never want exact pot odds because then you're always in EV neutral situations, which means no profit. You can play EV neutral pots for table image, but what you really want is pots with an overlay, thus a +EV situation for you.

Another use of the term is in $ guaranteed tournaments. Say a site offers a $100 guarantee prize pool on a $1+0 buyin. If 100 people enter, your share of the prize pool is 1%, exactly what you contributed. If only 50 people enter, you have a 2% share of the prize pool but only contributed 1%, thus you have a 1% overlay. Another very favorable situation. Assuming everyone in the tournament is of equal skill, this would be the only way to make money at MTTs in the long run.