When balanced twisted-pair copper cabling, return loss is a measurement of the:

Worst case difference in magnitude between the expected insertion loss and the actual measured insertion loss

Reflection of signal power resulting from the insertion of a device in a transmission line (in dB)

Signal coupling between any two pairs along the entire length of the cabling

Loss in signal resulting from the insertion of a component, of link, or channel, between a transmitter and a receiver

Time required for a signal to travel from one end of the transmission path to the other end