Brown dwarf
From Memory Alpha, the free Star Trek reference
A brown dwarf is a stellar object that has characteristics of both a star and a planet.
The Enterprise NX-01 wanted to investigate a brown star in 2152 when the ship was infested by a symbiotic lifeform and the investigation was interrupted. (ENT: "Vox Sola")
According to Data in 2366, the abundance of dysprosium in a brown dwarf star is different than regular stars, when factored with terbium, holmium, erbium, and europium. (TNG: "Manhunt")
