In telecommunication, in the modulation of a carrier, a significant condition is one of the values of the signal parameter chosen to represent information.

Note 1: Examples of significant conditions are an electrical current, voltage, or power level; an optical power level; a phase value; or a frequency or wavelength chosen to represent a "0" or a "1"; or a "mark frequency" or a "space frequency."

Note 2: The duration of a significant condition is the time interval between successive significant instants.

Note 3: A change from one significant condition to another is called a "signal transition."

Note 4: Signal transitions are used to create signals that represent information, such as "0" and "1" or "mark" and "space."

Note 5: Significant conditions are recognized by an appropriate device. Each significant instant is determined when the appropriate device assumes a condition or state usable for performing a specific function, such as recording, processing, or gating.

Source: from Federal Standard 1037C and from MIL-STD-188