The T'lli Beta system was a planetary system. The primary was named T'lli Beta. An inhabited planet in this system, T'lli Beta, was the homeworld for the T'lli Betans.
In 2367, the USS Enterprise-D was en route to the T'lli Beta system before it was ensnared by the gravitational pull of a cosmic string fragment which a group of two-dimensional beings were attempting to enter. (TNG: "The Loss")
The T'lli Beta system later appeared in the star chart Data and Picard were studying in stellar cartography in 2371, where it was located near the Lima Sierra system. (Star Trek Generations, display graphic)