Two white things appear on cigars. They are not friends. Plume (bloom) is a dry, powdery film of crystallized oils that can wipe off and does not smell of cellar rot. Mold is living: fuzzy, sometimes blue-green or grey, sometimes on the foot and wrapper, and it belongs in the bin, not on a tasting note.
The trade argues about how common true plume is. This page does not pretend to settle that. The practical test is texture and smell. Powder that dusts off a well-kept cigar is one thing. Spots with filaments are another.
Mold is a humidor problem: too much moisture, still air, or a wet sponge gone wrong. Keep relative humidity in a commonly cited range and give the box air. See humidors.