In telecommunication, a star coupler is a passive optical coupler having a number of input and output ports, used in network applications.

Note: An optical signal introduced into any input port is distributed to all output ports. Because of the nature of the construction of a passive star coupler, the number of ports is usually a power of 2; i.e., two input ports and two output ports (a "two-port" coupler, customarily called a "directional coupler," or "splitter" ); four input ports and four output ports (a "four-port" coupler); eight input ports and eight output ports (an "eight-port" coupler); etc.

Source: from Federal Standard 1037C and from the FAA Glossary of Optical Communications Terms

A star coupler was also the name of a device built by the former Digital Equipment Corporation of Maynard, Massachusetts. In this case, the medium was copper coaxial cable rather than an optical fiber, but the function was essentially the same. The signal that was distributed was 70 MB/s computer interconnect data and the star coupler provided two redundant paths of either 8 or 16 ports each. The star coupler was used with the VAX family of computers running the VMS operating system.