A line that bets once on the flop and checks after that.
The default line example for Air: c-bet once and give up if called. Example: with A♥ J♥ on a Q♠ 7♦ 2♣ board, bet the flop only, and check if called. Bet only when you're the raiser, the board favors your range (for example, Q-high or higher and dry), and the opponent is a player who folds.