The velum, derived from Latin velum, meaning a "sail", "curtain," "awning" or "veil," has several quite separate meanings in biology:

• the locomotory and feeding organ provided with cilia found in the larval stage called the veliger or "velum-bearing" stage of bivalves, such as mussels and oysters; or a delicate membrane found on certain Protists.
• the circular membrane round the cap of a sea jelly, or medusa of class Hydrozoa.
• the veil-like membrane of immature mushrooms extending from the margin of the cap to the stem and is torn by growth, revealing the gills of a mature sporophore; in a mature mushroom the remains of the velum may form an annulus or ring around the stem, familiar from common button mushrooms, and sometimes on the margin of the cap.
• the soft palate behind the hard palate.

• Velum is also a common misspelling of vellum, pigs skin with which books were once covered. Today, Leatherette, leather, cloth or paper are more commonly used.