Why the rating of motor is in KW or HP.

There is certain power factor already mentioned by the manufacturer due to impedence offered by the motor. So one can now the real power ...

You want to select a motor based on the shaft load you want to drive.

Electrical motor is a kind of rotating electrical machine whose purpose is to convert electrical (active) power into mechanical (work) power, so rated power of electrical motors is expressed in W, kW, MW or HP because of fact that this kind of power is a key factor for process of converting electrical (active) power into mechanical (work) power.

Rishi,

just to put together what Gary and Bojan say, the motor power is in kW (or HP) because it is the MECHANICAL power you get at the output shaft.

This means that the Power factor and all losses have been taken in account.

The motor power is expressed as P = sqrt(3).V.I.E.cos(phi)

E: Etta the efficiency.