When referencing the curve of a throw, the terms out-side in (OI) and inside-out (IO) are used. An OI throw is one that curves in towards the opposite side of the throwers body from which it is thrown. An IO throw is one that curves toward the same side of the throwers body from which it is thrown. With the rotation of the disc in mind, an IO throw has the side of the disc rotating toward the direction of the throw angled to the ground, whereas an OI throw has the side of the disc rotating toward the thrower angled to the ground. IO throws are generally the more difficult throw, and are very useful for breaking the mark.