The Omicron Theta system was a formerly inhabited remote star system.
Before 2328, colonists from Earth established the Omicron Theta colony on the planet Omicron Theta. The colony's primary mission was scientific in nature. A being known as the "Crystalline Entity" destroyed the colony, as well as all life on the planet, in 2338.
That year, a Federation cruiser, the USS Tripoli, was alerted to the colony by a signal. Tracing the signal to a signal device, a landing party discovered Data nearby. He been activated by the signal device after it detected the presence of the landing party members.
Twenty-six years later, in 2364, the USS Enterprise-D diverted its course briefly to this system in the search of answers as to Data's origins and the events leading up to the death of the colony. In the course of their investigations, they recovered the body of Lore. (TNG: "Datalore")