Tau Alpha C

From Memory Alpha, the free Star Trek reference.

Tau Alpha C was the homeworld of the humanoid species that The Traveler belonged to.

Tau Alpha C was many months away from Federation space even at maximum warp speeds; at warp 9.5 it would take exactly 123 days to reach the planet from near Starbase 133. It was estimated that the distance between Tau Alpha C and Starbase 133 is approximately 630 light years. (TNG: "Remember Me")

The Traveler, a native, visited the USS Enterprise-D crew in 2364, and he and Wesley Crusher worked together. (TNG: "Where No One Has Gone Before")

In an alternate universe created after Doctor Beverly Crusher became trapped within a warp bubble, Wesley tried to contact Tau Alpha C for assistance when individuals began disappearing from the Enterprise, with only Dr. Crusher noticing. Ultimately, the entire universe, including Tau Alpha C, disappeared. (TNG: "Remember Me")

Dr. Crusher mistakenly referred to Tau Alpha C as Tau Ceti in TNG: "Journey's End".