Bit of a mouthful, isn't it? But very important to game design. So, what is Orthogonal Unit Differentiation? In short, look at it as a term for multiple game elements having different functions when it comes to terms of gameplay. The most common example that comes up in Orthogonal Unit Differentiation is Chess Pieces - each piece can do something different, which in the end effects the endless strategic possibilities in the game itself. Tic-tac-to can be a simple example. What if instead of a 3x3 grid we gave a 5x5 or even a 10x10 grid? You earn points for every 3 in a row you have. What if we gave an additional element, like a square with an X or O that transforms anything next to it into an X or an O depending on what you are? Same with RPGs. You have 3 heroes, one that heals a target, one that taunts a target, and one that deals damage. As a player, you have your taunter get the attention your target enemy, you have your healer heal the taunter for the damage they take, and your damage dealer hurt the enemy. Adding additional elements only enhances the strategy (Taunter has a strong defend skill, damage dealer can put one target to sleep, healer can heal everyone once a battle, etc). Once you get past the jarble of words that is Orthogonal Unit Differentiation, you can see it's importance. What are some examples that you have of Orthogonal Unit Differentiation?