A backhand can be thrown at different angles when it is released at the end of the throw. The two main variations of the backhand throw are the backhand outside-in throw and the backhand inside-out. They are more commonly known as IO (inside-out) backhand and OI (outside-in) backhand.
Usually with regular backhand throws, the player is taught to have the disc as parallel to the ground as possible, especially when the disc is released. When the disc is parallel upon the release, it will be thrown straight at the target which is what people want. There are cases though when a defender is in the way and in order to get the disc to the cutter, the thrower will have to throw around the defender.
When throwing an IO backhand, the thrower should angle the disc so that the bottom of the disc is pointing inwards (or down) towards their own feet. Instead of swinging the arm away from the body, swing the arm downward (like a pendulum). The more perpendicular the disc is to the ground, the greater the curve of the disc's path when it travels to the cutter.
Keep practicing throwing at different angles to understand how they will affect the path of the disc.
When throwing an OI backhand, instead of having the disc parallel to the ground, the bottom of the disc should be pointing downward and away from the thrower's foot. The thrower's arm can be swung like how a regular backhand is thrown (parallel to the ground) but sometimes the arm can be leveled higher than shoulder height to help make the disc's path more curved. The more perpendicular the disc is to the ground, the greater the effect of the curve.
Keep practicing throwing at different angles to understand how they will affect the path of the disc.
To help players remember the difference between an IO and an OI is to remember that the bottom of the disc pointing inwards towards the feet is an IO (inside-out) and when the bottom of the disc is pointing outwards away from the feet, the throw is an OI (outside-in).
Another way to remember is at the beginning of the throw, if the disc is being thrown towards the body at first, it's an IO. If the disc is being thrown away from the body in the beginning, it is an OI.