Ernie
The KV number refers to revolutions per volt.
Example : a 370 e-flite brushless at 4100kv @ 10 volts will make 41,000 rpm
a 400 4200 kv @ 10 volt 42,000 rpm
I would have to assume that this number is based on free spinning with no prop.
I am no expert but this is what it says in the motor sheet