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

The velum is 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 velum is the circular membrane round the cap of a sea jelly, or medusa.

The velum is 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 velum is the soft palate behind the hard palate