Details:
A membrane raft that forms small pit, depression, or invagination that communicates with the outside of a cell and extends inward, indenting the cytoplasm and the cell membrane. Examples include any of the minute pits or incuppings of the cell membrane formed during pinocytosis. Such caveolae may be pinched off to form free vesicles within the cytoplasm. [GOC:mah, ISBN:0721662544, PMID:16645198]