Miss can mean:
1. Failing to make a drawing hand after all of the cards have been dealt. For example, if you hold A♠ K♠ and the flop comes 6♠ 2♠ 8♦, but the turn and river runs out 2♣ Q♦, you’ve missed your flush draw.
2. Can also refer to not connecting with the flop with any kind of made hand or draw. If you held A♠ K♠ and the flop came 6♥ 7♥ 8♦, you’ve missed the flop entirely.