A communication relay is a station that relays messages between various points, so as to facilitate communications between units.
When Colonial Heavy 798 and their escort, a Viper Mark II piloted by Lee Adama, encounters two Cylon Raiders en route to Caprica, Galactica receives DRADIS and communication via a nearby relay station (Miniseries).
After the Fall of the Twelve Colonies, Gina Inviere "helps" Kendra Shaw locate and identify a communications relay used by the Cylons. During the planning stages of this attack, Lieutenant Colonel Jack Fisk notes that the relay looks like a "frakked up can opener", and Admiral Helena Cain decides to engage this target because it is considered a light target. Upon executing their attack plan, it becomes apparent that the communications relay they attack is a staging area and that Inviere has lead them into a trap, resulting in heavy losses of both military assets and personnel ("Pegasus", "Razor").