A solarium was a type of structure designed to let in ample sunlight.
In 2373, the New Essentialists staged a raid on a solarium in the resort located at Temtibi Lagoon on Risa, so as to demonstrate the vulnerability of the Federation. (DS9: "Let He Who Is Without Sin...")
Shortly before Ezri Dax's visit in 2375, the Tigan family installed a new solarium in their house on Sappora VII, with tiles brought in from Andoria. (DS9: "Prodigal Daughter")