The Triangulum system was a star system.

In 2366, after Worf declared that he could not find any trace of those responsible for decimating the Rana IV colony, Captain Jean-Luc Picard recalled a Starfleet admiral who had had difficulty locating some renegade Andorians in the Triangulum system. It turned out that the Andorians dismantled their ship in order to hide it. (TNG: "The Survivors")

This system was only mentioned in dialogue.
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