In telecommunication, the term loop gain has the following meanings:
1. The total usable power gain of a carrier terminal or two-wire repeater.
Note: The maximum usable gain is determined by, and may not exceed, the losses in the closed path.
2. The sum of the gains, expressed in dB, acting on a signal passing around a closed path, i.e. , a loop.
Source: from Federal Standard 1037C and from MIL-STD-188
