In physics, the principle of a generator is that the magnetic field changes in a closed wire. So the copper wire you mentioned in the generator is the enclosed conductor that the generator uses to generate electrical energy.
What is precise is not the quantity of copper wire. This should be the number of turns and the diameter of the copper wire. When the rate of change of the magnetic field is constant, the more turns, the higher the voltage. The thicker the copper wire, the greater the current it allows to flow.