A waveform shape with squared corners. Unlike the continuous nature of sine waves, square waves have very fast (infinitely fast in theory) rise and fall times with periods of steady state voltage at the top and bottom.There is no way for a theoretically perfect square wave to exist because in practice it always takes some amount of time for the voltage swing from the bottom to the top (and top to bottom) to occur. A waveform shape does not have to be a perfect geometric square to be considered a square wave, but in general they do approximate the shape. In practice we tend to call many waveforms that have really fast rise and fall times with roughly equal periods of steady state between them square waves, though there are some other more specific (and correct) names for a few of the variants. Square waves are used in all kinds of digital equipment because they are ideal for representing the ones and zeros of digital. They are also used for clock and other data signals as well as certain types of audio signals. In audio, square waves have a very specific type of harmonic structure and thus a very distinctive sound to them. An instrument such as the clarinet naturally creates something very close to a square wave, and in synthesizers square waves are used to emulate clarinets. Also, a sine wave that is in severe clipping begins to take on a square like quality. In fact, most waveforms (even very complex ones) begin to exhibit some of the characteristics of square waves under severe clipping.