View source for Glossary (Mario Tennis: Power Tour)

===O===
*'''On The Line'''- A ball that lands on a sideline or baseline. It is considered to be in bounds.
*'''One-Up/One-Back'''- A doubles formation used to defend the court. Players divide the court into the fore-and backcourts. The rear player is in charge of offensive attacks.
*'''Open Court'''- The are on the court outside the area the player is defending. Also called open space.
*'''Out of Bounds'''- When the ball is hit outside the boundaries of the court.
*'''Over Court'''- Hitting the ball out of bounds beyond the opponent's baseline.
*'''Over Net'''- Letting the racket cross the net before hitting the ball.