In basketball, And-One refers to when a player is fouled while attempting to shoot a ball and the ball goes in the basket.
The player is awarded one free throw, allowing him to score 3 points in total if he can shoot the ball into the basket during such a free throw.
The term originates from players yelling out ‘and-one’ after a field goal lands and they feel that they have been fouled but the referees did not make the call.