A fusor, according to a proposal to the IAU by Gibor Basri, Professor of Astronomy at the University of California, Berkeley to help clarify the nomenclature of celestial bodies, is "an object that achieves core fusion during its lifetime". This definition included any form of nuclear fusion, so the lowest possible mass of a fusor was set at roughly 13 times that of Jupiter, at which point deuterium fusion becomes possible. This is significantly smaller than the point at which sustained hydrogen fusion becomes possible, around 60 times the mass of Jupiter. Objects are considered "stellar" when they are about 75 times the mass of Jupiter, when gravitational contraction, i.e. contraction of the object due to gravity, is halted by heat generated by the nuclear reaction in their interiors. Fusors would include active stars, dead stars, and brown dwarfs.
The introduction of the term "fusor" would allow for a simple definition:
where round is understood as "whose surface is very nearly on the gravitational equipotential", orbits means "whose primary orbit is now, or was in the past around", and capable implies fusion is possible sometime during the existence of the object by itself.