Kv is a measurement of performance. Think of how full-size manufacturers try to impress us with big horsepower numbers. While Kv isn’t horsepower, it does allow us to compare a performance attribute of motors. Specifically, Kv is how fast (rpm) a motor spins when one volt is applied to it. So, in theory, the higher the Kv rating, the faster the motor. For example, a 9000Kv motor would be considerably faster than a 2200Kv motor.
If Kv made us think of horsepower, turns reminds us of displacement. That is to say, like displacement, turns is a physical attribute of a motor. The number of turns indicates how much wire is wrapped inside the motor. A higher turn number means more wire which means more resistance which means a slower motor. So, turns is just the opposite of Kv in the sense that with turns a lower number means faster. For example, 4.5-turn motor would be considerably faster than a 15.5-turn motor.
When you want to buy a new brushless motor for your RC truck, it’s only natural and pretty prudent to want to compare offerings from different brands. The only problem is the manufacturers don’t make it easy. Some market their motors by Kv rating and others use the term turns.