Referring to the extent to which a signal attenuates, or loses power across an interface between two components, e.g., from the input side of the interface between a circuit and a switch or router to the output side of the interface, or from the output endface of one optical fiber to the input interface of another across a pair of connectors. Coupling loss, or coupling inefficiency, is generally described as insertion loss, as measured in decibels (dB). See also coupling efficiency, dB, insertion loss, and signal.