What is Cycle
When a waveform reaches a complete set of positive and negative value it is called one cycle., such as if a sinusoidal wave, completes one set of positive and negative values, is called one cycle of sine wave cycle. One cycle is corresponding to the angular measure of 360 deg.
Refer the Example sin wave:
Take the electrical quantity voltage or current in y-axis and time or angle in the x-axis. In this, a sin wave has the complete Positive half cycle from 0 deg to 180 deg and the complete negative half cycle from 180 deg. To 360 deg. Combination of Both positive and negative half cycle is called one complete cycle.
Note: A complete cycle may not have 360 deg of the waveform. But it should have one positive and negative half cycle.