Outs

math

Cards remaining in the deck that improve your hand to a winner.

Rule of 2 and 4: outs × 2 = roughly your % to hit on the next card; outs × 4 = your % from flop to river (when calling all-in).

See also

Equity
Your statistical share of the pot, expressed as a winning probability.
EV
The average profit/loss of a play over infinite repetitions.
Implied Odds
Pot odds adjusted for expected future bets if you hit your draw.
Pot Odds
The ratio of the current pot to the cost of calling.