1-and-1 or 1-plus-1.

In college and high school Basketball a free-throw attempt awarded for certain violations that earns the shooter a 2nd. attempt only if the first is successful.

One-on-one.

Describes a situation in which an offensive player has possession of the ball and is attempting to score against a single defender. The two opposing players confront one another with no assistance from teammates. It may arise on a one-player fast break against a single defender or when a team has cleared out the side of the court where the ball is located.

One Shot.

Last shot at the end of quarter and half.

Open or "Open Man".

When a player is unguarded by a defender. An unguarded player.

Open Shot.

A shot taken by an undefended player.

OT.

Abbreviation for overtime.