Sub-brown dwarf

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A size comparison between our Sun, a brown dwarf, and Jupiter.

Sub-brown dwarfs or brown sub-dwarfs are objects only faintly visible in large telescopes

Their inferred masses are smaller than the low-mass cut-off for brown dwarfs.
They are colder than stars undergoing nuclear fusion.

Their status is somewhere between giant planets and proper stars, but they are referred to as planets by some astronomers.

However, a sub-brown dwarf is formed in the manner of stars, through the collapse of a gas cloud, and not through accretion or core collapse from a circumstellar disc. The distinction between a sub-brown dwarf and a planet is unclear; astronomers are divided into two camps as whether to consider the formation process of a planet as part of its division in classification. ^[1]

An alternate definition involves the same mass range (less than a brown dwarf, but in the planetary range), but is free of gravitational attachment with any star. These are generally referred to as free-floating planets. Though less popular, this usage is in the IAU Extrasolar Planets provisional definition of a planet.