1. In dermatology, a vesicle is a small blister, as on the skin.

Vesicles also occur on the mucous membranes; such as, the buccal mucosa (the lining of the mouth).

2. In anatomy, a vesicle is any small pouch; for example, the seminal vesicles are a pair of pouch-like structures located behind the bladder and above the prostate gland that contribute fluid to the ejaculate.
3. A small bulla, as seen in herpes simplex or chickenpox.
4. Etymology: the word vesicle comes from the Latin diminutive vesiculum, meaning "a small bag" or "bladder".