The Brechtian Cluster was a region of space containing two inhabited planets. In 2368, all life on those planets were threatened by the Crystalline Entity. The USS Enterprise-D was able to intercept the Entity before it reached the Brechtian Cluster. (TNG: "Silicon Avatar" ) The Star Trek Encyclopedia (4th ed., vol. 1, p. 102) identified the Brechtian Cluster as a star system. "Brechtian" is a word refering to the literary style of Bertolt Brecht