PMO or planetary mass object (which is also sometimes used for objects orbiting stars: the word planet could be used, but the phrase perhaps suggests an absence of knowledge about the object.)
isolated PMO or isolated planetary mass object (IPMO), clearly indicating it is not part of a stellar system.
MACHO which is also meant to include brown dwarfs and perhaps any unsuspected populations of dim stars.
sub-brown dwarf - within the mass-range of planets, but the term suggests it is star-like, the results of star formation producing a lower-mass object, rather than the results of typical planet formation within a protoplanetary disk.
Like all exoplanets, they are challenging to detect and observe,
and the effective exoplanet detection methods based upon observing the
host star do not apply.
Nearby candidates are observable IR sources,
and gravitational microlensing can turn up candidates.
With the ongoing improvement of observation equipment, candidates
are being discovered, largely within the last decade or two.
Invariably the question arises whether the candidate is actually a
brown dwarf: there is always uncertainty regarding the object's
mass and internal characteristics that would classify it.
An example candidate is WISE 0855-0714.