Generally speaking they are the same thing. A 240VAC circuit is its maximum. The 220VAC number is usually followed by the term RMS (Root Mean Square). This is based on the fact that power is transmitted to our homes as an AC wafeform (60Hz here in Canada and the US). Although the peak-to-peak value is 240V when you take the RMS of the waveform it gives you the smaller number. Although somewhat simplified you can think of the 220V as the average of the 240V peak-to-peak AC waveform.