"cuticle" is one term used for the outer layer of tissue of a mushroom's basidiocarp, or "fruit body". the alternative term "pileipellis", latin for "skin" of a "cap" (meaning "mushroom") might be technically preferable, but is perhaps too cumbersome for popular use. it is the part removed in "peeling" mushrooms. on the other hand, some morphological terminology in mycology makes finer distinctions, such as described in the article on the "pileipellis". be that as it may, the pileipellis (or "peel") is distinct from the trama, the inner fleshy tissue of a mushroom or similar fruiting body, and also from the spore-bearing tissue layer, the hymenium.