According to the IAU decision of 2006 a planet is a celestial body which:
is in orbit around the Sun,
has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
has “cleared the neighbourhood” around its orbit.
and an exoplanet is a planet around another star.
So what is this?
Looks likes a planet, definitely not a star. It’s bigger than Jupiter, but not big enough to be a brown dwarf (a brown is technically a star). But it doesn’t go around a star. Instead it seems to wander lost through space. It’s bigger than Jupiter, but not big enough to be a brown dwarf (a brown is technically a star). So what word should use to describe it?