Alternating Current is the movement of electrons in a wire backwards then forwards repeatedly. In Europe this change repeats 50 times per second (or 50 Hz). In the USA, the frequency is 60 Hz.
AC is remarkably useful because it allows us to change electricity very easily using transformers which cannot work with DC.
If we connect an oscilloscope (a voltmeter which shows a graph of how voltage varies with time) to an AC power supply, we would see a graph like this:.