1. In data transmission, a functional unit that permits a common path to handle more data sources than there are channels currently available within the path.
Note: A concentrator usually provides communication capability between many low-speed, usually asynchronous channels and one or more high-speed, usually synchronous channels. Usually different speeds, codes, and protocols can be accommodated on the low-speed side. The low-speed channels usually operate in contention and require buffering.
2. A device that connects a number of circuits, which are not all used at once, to a smaller group of circuits for economy.
Source: from Federal Standard 1037C and from MIL-STD-188