What does "vesicle" mean?

Vesicle: A bladderlike vessel; a membranous cavity; a cyst; a cell. Specifically: --(a) (Bot.) A small bladderlike body in the substance of vegetable, or upon the surface of a leaf. (b) (Med.) A small, and more or less circular, elevation of the cuticle, containing a clear watery fluid. (c) (Anat.) A cavity or sac, especially one filled with fluid; as, the umbilical vesicle. (d) (Zoöl.) A small convex hollow prominence on the surface of a shell or a coral. (e) (Geol.) A small cavity, nearly spherical in form, and usually of the size of a pea or smaller, such as are common in some volcanic rocks. They are produced by the liberation of watery vapor in the molten mass.