A circumplanetary disk is a disk surrounding a planet
analogous to a circumstellar disk around a star.
These are theorized and there exist candidates for such disks around
known extra-solar planets.
They are presumed to occur in young systems and presumed to be a
significant source of moons.
Saturn's ring system can be classified as a circumplanetary disk
of sorts, but the term was likely coined for disks occurring around the
time of a planet's formation, i.e., when its moons generally formed.
Saturn's rings are thought possibly to be leftovers from such a
disk, or possibly debris from moons, broken up by impact
or tidal force.