Impedance is a measure of how much an electical circuit resists the flow of electricity.

The signal provided by a security camera will meet a level of impedance when it is plugged into a channel of a DVR. Problems can arise when a single security camera is plugged into multiple (any more than two) channels because the camera is not strong enough to overcome the impedance of all the circuits.

Impedance is also a factor when the wire cable connecting a security camera to DVR is very long.