Actually that is only the measure of the speed of the motor. Kv is rpm per volt, so a 2200 kv motor on 1 volt would probably do around 2200 rpm. The other measure is for size, and that is all of the numbers before the kv, like 2204 or 2218. The first number is width and the other is height I think. Also for size measurements some brands measure the actual motor dimensions, while others measure the stator, so 2 2218 motors from different brands can be different sizes, and a motor with larger measurements might actually be smaller. For example, I have a 2218 motor from Emax and a 2826 from NTM. The NTM's measurements are bigger, but the Emax motor is actually larger and it is probably more powerful. Sadly there is no standard for where to measure from, so you just gotta be careful and do proper research before buying.