Caveola: An tiny pit, grotto, depression, incupping in the surface of a cell. The name "caveola" means little cave. The plural is caveolae.
Caveolae normally function to facilitate the uptake of fluid by the cell. In the process of pinocytosis, the caveolae close and pinch off to form pinosomes, little fluid-filled bubbles within the cell.
Bacteria can hide in caveolae. Normally when bacteria enter cells, they go into compartments that fuse with cell structures called lysosomes in which they are destroyed. Caveolae do not fuse with lysosomes. The bacteria nestled in a caveola can thus escape extermination.