Lazon II, the second planet in the Lazon system.
Lazon II was originally planned as a deutronium mining colony for the Cardassians. When demand for the fuel dropped, the site was turned into a labor camp. (TNG novel: Triangle: Imzadi II)
In 2371, Thomas Riker was imprisoned there for attacking several Cardassian targets with the USS Defiant, which Riker had stolen from Deep Space 9. (DS9 episode: "Defiant")
Later in 2371, Sela freed Riker from Lazon II, although he was later returned there. (TNG novel: Triangle: Imzadi II, TNG - Slings and Arrows eBook: A Weary Life)
Kyle Riker thought Thomas could have been released by the Cardassians prior to 2379, although Will Riker had heard nothing. (ST novel: A Time to Hate)
In an alternate timeline, Lazon II was invaded by the Grigari. (DS9 - Millennium novel: The War of the Prophets)