A square wave is a kind of non-sinusoidal waveform

Non-sinusoidal waveform

Non-sinusoidal waveforms are waveforms that are not pure sine waves. They are usually derived from simple math functions. While a pure sine consists of a single frequency, non-sinusoidal waveforms can be described as containing multiple sine waves of different frequencies. These "component" sine...

, most typically encountered in electronics

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 and signal processing

Signal processing

Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...

. An ideal square wave alternates regularly and instantaneously between two levels. Its stochastic counterpart is a two-state trajectory

Two-state trajectory

A two-state trajectory is a dynamical signal that fluctuates among two distinct values . In most applications, the signal is stochastic; nevertheless, it can have deterministic ON-OFF components...

.
Square waves are universally encountered in digital

Digital

A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

 switching circuits and are naturally generated by binary (two-level) logic devices. They are used as timing references or "clock signal

Clock signal

In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome to coordinate actions of circuits...

s", because their fast transitions are suitable for triggering synchronous logic circuits at precisely determined intervals.