RcPaul, the kv rating on a motor is under a no load.
If you know the kv of a motor it gives you an idea of what to expect from the motor on a given prop and voltage in.

This number is the motor voltage constant expressed in RPM/Volt. This indicates how fast the motor will turn for a given voltage (given there is no internal resistance). As an example, a motor rated at 4300Kv rating is 4,300 RPM/Volt. Therefore, if a 6.0-volt battery pack is used, the RPM would be 25,800 (6.0 x 4,300).

Also with knowing this info you can figure the Watts out. This will also help know how the plane will proform.

Paul, seems I'm just around the corner from you. I live over by Polaris. Just a hop and a skip. If you want to go fly together let me know. Always welcome.
Hope this helped to understand the Kv rating for you. BG