The island named in the Tamarian phrase about Darmok and Jalad, a story of two strangers who become allies by facing a common danger together.
Tanagra is a place in Tamarian mythology, central to the Next Generation episode Darmok.
The Children of Tama speak entirely in references to their own stories. Captain Dathon repeatedly offers Picard the image of Darmok and Jalad at Tanagra, and has both captains beamed to the surface of El-Adrel IV, where a dangerous creature roams.
Research by Data and Troi turns up Tanagra as an island-continent on the planet Shantil III. Picard gradually understands the tale: two men arrived separately on the island, fought a beast together and left as friends. Dathon had hoped to recreate it, and gives his life in the attempt.