Difference between "planetary ring" and "circumstellar disk"?
From Physics SE:


  A circumstellar disk is a set of objects that orbit about a star-like object and that collectively look disk-like in some way.


From Wikipedia:


  A ring system is a disc or ring orbiting an astronomical object that is composed of solid material


So, a circumstellar disk may have gas, dust, asteroids, etc., but it must orbit a star-like object. A ring system must have something solid--dust or moonlets--but it may orbit any astronomical object.

Other than that, you specifically asked about a planetary ring. That would mean a ring system that specifically had a planemo as the central body.

In other words, a disk around a brown dwarf could be described as a circumstellar disk (a brown dwarf is a star-like object) or a ring system (as long as the disk contained solid material). It could not be called a planetary ring, because a brown dwarf is not a planet.