In Ultimate frisbee, a throw that is thrown in the direction you are facing, but curves in the opposite direction. So a backhand thrown by a right hander would be thrown to the left(since a backhand is thrown from the left side of a right hander) and would curve right. This is useful for throwing down the sideline, around defenders and many other things. Be sure to get lots of spin on an outside in throw so that it doesn't blade into the ground. The best way to catch an outside in throw is if you can get a hand on the inside of the disc, so that if the spin causes the disc to bounce off your hand, it will bounce right into your body.

Outside in is the opposite of inside out.