SQUARE WAVE

On an oscilloscope, a theoretically perfect square wave would look like a pair of parallel dotted lines, one having positive polarity and the other having negative polarity (Fig. 1a). In real life, the transitions often can be seen as vertical lines (see Fig. 1b).

Fig. 1. (a) A theoretically perfect square wave. (b) The more common rendition.

A square wave might have equal negative and positive peaks. Then the absolute amplitude of the wave is constant at a certain voltage, current, or power level. Half the time the amplitude is +x, and the other half it is -x volts, amperes, or watts.
Some square waves are asymmetrical, with the positive and negative magnitudes differing. If the length of time for which the amplitude is positive differs from the length of time for which the amplitude is negative, the wave is not truly square but is described by the more general term rectangular wave.