In Ultimate frisbee - a throw that, as a backhand, a throw to the right that curves left; as a forehand, a throw to the left that curves right.

Taken from the Ultimate Handbook,

Note that this only applies to right handers. This can be achieved by dipping the outside edge of the disc as you are throwing it. Throwing slightly inside out can improve the stability of your throws. Catching an inside out throw is easiest if you can get your hand on the outside of the disc, due to the direction the disc is spinning.