A map of the de Laure belt
The de Laure belt is a region of space where the Tau Cygna system is located.
The USS Enterprise-D was on a mission in the belt in early 2366 to evacuate a Human colony from Tau Cygna V as the planet was claimed by the Sheliak Corporate. (TNG: "The Ensigns of Command")
It is unclear whether the writers of the episode intended "Tau Cygna" to be Tau Cygni, a real binary star approximately 69 light years away from Sol.