Signal transition
Signal transition: In the modulation of a carrier, a change from one significant condition to another.Note 1: Examples of signal transitions are a change from one electrical current, voltage, or power level to another; a change from one optical power level to another; a phase shift; or a change from one frequency or wavelength to another.
Note 2: Signal transitions are used to create signals that represent information, such as "0" and "1" or "mark" and "space."
Source: from Federal Standard 1037C
