In mycology, a partial veil is a temporary structure of tissue found on the fruiting bodies of some basidiomycete fungi, typically agarics. Its role is to isolate and protect the developing spore-producing surface, represented by gills or tubes, found on the lower surface of the cap. A partial veil, in contrast to a universal veil, extends from the stem surface to the cap edge. The partial veil later disintegrates, once the fruiting body has matured and the spores are ready for dispersal. It might then give rise to a stem ring, or fragments attached to the stem or cap edge. In some mushrooms, both a partial veil and a universal veil may be present.

An annulus is the ring-like or collar-like structure sometimes found on the stipe of some species of mushrooms. The annulus represents the remnants of the partial veil, after it has ruptured to expose the gills or other spore-producing surface. It can also be called a ring which is what the Latin word annulus directly translates as. The modern usage of the Latin word originates from the early days of botany and mycology when species descriptions were only written in Latin. Outside of the formal setting of scientific publications which still have a Latin requirement, it will often just be referred to as a ring or stem ring in field guides and on identification websites.