A small device for connecting two cables to make a longer cable, sometimes called an inline coupler. Inline couplers do not provide any amplification or signal boost, and can cause attenuation and signal degradation unless they are of high quality. One example would be a small box that accepts two category 5 (CAT5) cables with RJ-45 connectors and links them to form a longer cable.
Another example would be the BNC barrel connector for joining two lengths of thinnet cabling. A third example would be a coupler with two RJ-11 connectors for joining two phone lines.
The term «coupler» is also used to refer to modular connectors that can snap into customizable patch panels to allow different kinds of cabling to be mixed in one patch panel.
A category 5 UTP (unshielded twisted-pair) coupler.