The time it takes for a signal to travel through a circuit, piece of equipment, or a length of cable. When the luminance and colour information of a video signal are separated for processing, then reunited at the output of a device, it is critical that the propagation delay for each signal component is equal or distortion similar to ghosting will result. Propagation delay is most noticeable in color-under VHS players.

Propagation delay is also a problem when routing computer data and clock signals around a chip or circuit board. The faster the clock, the more critical the path delays.