A) The time required for a signal to pass through a device or conductor.

b) The time it takes for any circuitry or equipment to process a signal when referenced to the input or some fixed reference (i.e., house sync).

Common usage is total delay through a switcher or encoder. c) The amount of time between input of the first pixel of a particular picture by the encoder and the time it exits the decoder, excluding the actual time in the communication channel. It is the combined processing time of the encoder and decoder. For face-to-face or interactive applications, the delay is crucial.

It usually is required to be less than 200 milliseconds for one-way communication.