- (anatomy) A small sac or cyst or vacuole, especially one containing fluid. A blister formed in or beneath the skin, containing serum. A bleb.
- A small bladder-like cell or cavity.
- (geology) A small cavity formed in volcanic rock by entrapment of a gas bubble during solidification.
- (cytology) A membrane-bound compartment found in a cell.
- (anatomy) A pocket of embryonic tissue that is the beginning of an organ.