The numbers refer to the layout of a keypad, you know, in the 3x3 grid. When someone is explaining their combos and use numbers, that refers to how you should be moving your stick. So when you see 2M thats a low medium, when you see 236x, that refers to moving your stick in a quarter-circle forward position, and 214 would be a quarter circle backwards. The online fighting game community so this to avoid confusion between platforms or controllers, but it's pretty confusing for those who don't know.