Definition of Air
In poker, the term "air" refers to when a player has a worthless hand.
The most common usage of the term occurs when a player bluffs another player out of a pot holding a worthless hand.

You decide to reach for some chips to put in a re-raise. After sliding out a large stack of chips, you notice your opponent looking pained. After a few moments of thought, he folds his A-J face-up. You proudly show your 2-3 offsuit and take down the pot.
In this case, you bluffed your opponent with "nothing but air".
It goes without saying that you should have a great read on your opponent if you plan on bluffing them with nothing but air.
--
Recent Articles That Include The Term Air:
Pokerstars Introducing New Rewards Program; To Include "Select" and "Select+" Tiers
An Update on Shaun Deeb's $1 Million Weight Loss Bet
GGPoker Issues Apology After Embarrassing "Superuser" Incident
Garrett Adelstein vs Robbi Jade Lew Hand Explodes Into Mainstream Media
World Poker Tour Launches New "WPT Prime" Series
Back to the - Poker Dictionary