The veil is a protective membranous tissue surrounding the hymenium (and even the whole fruiting body) of the immature mushroom of many cap fungi. In mushrooms and fly agarics, for example, the skirt-like ring along the stalk is a remnant of the veil that ruptures when the cap grows into an adult mushroom.
Sources
Wikipedia – Veil or Velum 
Unsplash – Photo of mushrooms
April 2023, TÄNKOM | Revised May 2025 RETHINK
