What does alveolus mean?
The definition of alveolus
Al*ve”o*lus, n.; pl. Alveoli.
Etym: [L., a small hollow or cavity, dim. of alveus: cf. F. alvéole. See Alveary.]

1 A cell in a honeycomb.
2 (Zoöl.)
A small cavity in a coral, shell, or fossil
3 (Anat.)
A small depression, sac, or vesicle, as the socket of a tooth, the air cells of the lungs, the ultimate saccules of glands, etc.