lveolus (plural, alveoli) is a small hollow or cavity; A Microscopic air sac in the lungs.
Alveoli are the air sacs located at the ends of the bronchioles inside the lungs.
Lining of the lungs can be folded into numerous small sacs called alveoli.
The adult human lung contains over 200 million alveoli.
Because of the enormous number of alveoli, the surface area of the lung is very large.
Alveoli increase the internal surface area of the lungs, consequently increasing the amount of oxygen that can be absorbed.