Mold

Mold belongs to the fungi, and UF/IFAS Extension's EDIS glossary describes that kingdom: organisms that are single-celled or form bodies of tubular hyphae, reproduce by spores, and secrete digestive enzymes and re-absorb nutrients.

EPA's mold guide describes what mold does outdoors: molds are part of the natural environment and break down dead organic matter such as fallen leaves and dead trees. Their spores are invisible to the naked eye and float through outdoor and indoor air, and there are many types of mold, none of which will grow without water or moisture.

Eagle Roofing Products, a concrete tile manufacturer, names mold plainly in its own list: a buildup of algae, mold and mildew on concrete tile is typical of all natural materials, and while these biological pollutants are not harmful to the tile's integrity, some owners find the appearance undesirable.

ARMA's bulletin uses the word as a comparison rather than a diagnosis: the black discoloration and streaks on many roofs are often mistaken as mold or mildew and are actually algae. The black streaks on a Naples roof are described on the roof cleaning page, and how algae differs from mold on a roof is its own answer, algae versus mold on a roof.

The word closest to mold in everyday use is mildew, and UF/IFAS Extension collapses the distance: mildew is mold, and both grow from spores which exist almost everywhere. The mildew glossary entry covers how the two words are used, can mildew grow on a metal roof takes up painted metal, and why everything in Naples grows mildew is its own answer.

Mold is one of several growths on a roof that reproduce by spores, and the glossary entry for spores covers the word on its own.

EPA's description is not tied to one surface: mold spores float through outdoor air, and no mold grows without water or moisture. What mold on pavers means, and whether it comes off, is its own question, can mold be removed from pavers.