The same of what Andy says above in details and with full equations.
In electrical terms, the average (or mean) value of a periodic waveform is also known as the DC level of the waveform, even if it is zero.
For example if you will try to charge a battery with a bipolar and symmetrical waveform, then there is no net charge on battery.
So the average of the above waveform is
However, it is not the average current (or voltage) of an AC which determines its power delivering capability. The RMS value for a voltage or current waveform is the effective value from the point of view of power dissipation in a resistive circuit.
So the effective or RMS current will be
But I have a question here: How we can apply
A practical use of the above is in rectifier circuits, that is shorten the contact time of diode, the power dissipation decreases but RMS current remains the same!