Definitions for "Copper loss"
Also referred to as I2R loss, this is the power dissipated in the coil when current is flowing. As the second term implies, the power dissipated is the load current squared times the DC resistance of the coil. This is valid for low frequencies, such as 50 Hz (European commercial power) and 60 Hz (American commercial power) but gets more complicated as the frequency goes up. The overall effect is still copper loss but there are other effects at higher frequencies. See proximity effect and skin effect.
The energy wasted as heat in the copper (or aluminum) windings, as copper/aluminum is not a perfect conductor of electricity.
The power loss (PR) or heat generated by current (I) flowing in a winding with resistance (R)