A brown dwarf is a self-gravitating object too light to sustain ordinary hydrogen fusion. Electron degeneracy limits its contraction, leaving radii near that of Jupiter across a broad mass range.
The conventional deuterium-burning boundary is near Jupiter masses, with composition-dependent variation. It is a useful classification scale rather than a sharp formation-based distinction between planets and brown dwarfs.
The hydrogen-burning minimum mass is the lowest mass that can sustain core hydrogen fusion, about -- solar masses for near-solar composition. Less massive brown dwarfs cool continually after any deuterium burning ends.
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A brown dwarf is a type of celestial object that falls between the largest planets and the smallest stars in terms of mass. Specifically, brown dwarfs have masses ranging from about 13 times the mass of Jupiter (approximately 0.012 times the mass of the Sun) to around 80 times the mass of Jupiter (about 0.07 times the mass of the Sun). They are not massive enough to sustain hydrogen fusion in their cores, which is the defining characteristic of true stars.