The time interval between the propagation of a signal and its reception; the time taken for a pulse to traverse any electronic device or circuit. In a switching transistor, for example, it is the time between the application of a pulse to the input and the appearance of a pulse at the output. Excessive pulse rise and fall times can reduce the speed of operation of a switching circuit and lead to undesirable delay. A known delay may be introduced into a system deliberately, by means of suitable delay line.