Celos (pronounced KEL-ohs) was the name of two different planets in the Milky Way Galaxy. (Star Trek: Arcadia)
One planet lay along the Alpha-Beta Quadrant border. In the 23rd century, it was part of territory hotly contested between the Klingon Empire and the Federation.
Another was home to a scientist who studied the planet Horuulk in the Romulan Neutral Zone before 2382.