Question: what is the difference between the words alveolus and alveoli?
Answer: An alveolus (plural: alveoli) is a word used in anatomy for hollow cavities, which are empty areas within a body. Although there are many different types of alveoli in the body, the word alveoli is usually used to talk about small air sacs in the lungs of mammals. These are also called pulmonary alveoli.