The term delay line has multiple meanings:

• In telecommunication:
  • A delay line is a transmission line, or equivalent device, used to delay a signal.
  • A single-input-channel device, such as a single-input sequential logic element, in which the output channel state at a given instant, t, is the same as the input channel state at the instant t−n , where n is a number of time units, i.e., the input sequence undergoes a delay of n time units, such as n femtoseconds, nanoseconds, or microseconds. (Note: The delay line may have additional taps yielding output channels with values less than n.)
• In computing, delay line often refers to delay line memory.
• In digital signal processing, as in telecommunications, a delay line refers to a sequential logic element in which the output state at a given time n (in samples) is the same as the input was at the time n−L. Delay lines are generally expressed as z^-L, where L is the length of the delay in samples. A unit delay (a delay of one sample) is therefore expressed as z^-1.
• In neurobiology, delay lines can refer to neurons, the cells that transmit electrical information in the brain. Electrical conduction in neurons is not instantaneous, it is delayed depending on the length of the axon and other properties of the neuron (e.g. myelination). This delay can be used for time sensitive calculations; the canonical example is the calculation of inter-aural time differences in the pons, used for sound localization.

An earlier version of this page came from Federal Standard 1037C and from MIL-STD-188.