Delos IV was a planet located in the galaxy's Alpha or Beta Quadrants, the fourth planet in the Delos star system in Federation space.
Doctor Beverly Crusher served her medical internship on Delos IV, under Dr. Dalen Quaice. (TNG episode: "Remember Me")
Quaice described Delos IV as "the hottest, driest place in the galaxy" and that it made "a Vulcan desert look like a rain forest". (TNG novel: Reunion)