An optical data network (or ODN) was a system of fiber optic cables on board starships and space stations that was used for data transfer between computers and remote terminals. There were large bundles of optical cables connecting the redundant computer cores.
In 2368, a Satarran starship's advanced sensor system was able to match the frequency of the USS Enterprise-D's optical data network in order to access the ship's computer system. After the Satarrans are able to erase the memories of the crew, Geordi La Forge was successfully able to access the optical data network for the engineering core in order to monitor every system routed through it. (TNG: "Conundrum")