Square Wave:

On an oscilloscope, a hypothetically perfect square wave would seem like a pair of parallel dotted lines, one containing positive polarity and the other containing negative polarity (the figure is as shown below). In real life, the transitions frequently can be seen as vertical lines (the figure is shown below).

Figure: (a) A theoretically perfect square wave. (b) The more general rendition.

A square wave may have equivalent positive and negative peaks. Then the absolute amplitude of the wave is steady at a certain current, voltage, or power level. Half the time the amplitude is + x, and in another half it is - x volts, amperes, or watts.

Some of the square waves are asymmetrical, with the negative and positive magnitudes differing. When the length of time for which the amplitude is positive differs from the length of time for which the amplitude is negative, then the wave is not truly square though is explained by the more common term rectangular wave.