A generic term for a variable rectangular waveform that varies between high (+) and low (-). The square wave is a pulse wave with a 1/2″ (50%) duty cycle, therefore the value of every even-numbered harmonic is zero. A pulse wave with a duty cycle of greater than 1/2″ has the same spectrum as a pulse wave whose duty cycle has the same denominator (e.g., a 1/3 has the same spectrum as a 2/3 duty cycle.)

See PWM, Appendix C.