(2) In time measurement, duty cycle is defined as the ratio of the duration of the phenomenon in a given period to the period, where duty cycle is abbreviated as D. In electronics, for example the duty cycle would refer to the period of time in which the device operates without negative effects (e.g. the period of time a power supply would run without overheating).
(3) In RF (radio frequency) the duty cycle, also called the duty factor, is the measure of the fraction of the time a radar is transmitting.