An alveolus (noun) is a gathering of alveolar people. (See alveolar.) The gathering can either be informal or a formal meeting arranged as part of an official alveolar group or association.
Because alveolar people are whiny and neurotic, spending a lot of time at an alveolus typically induces major headaches, sometimes even debilitating migraines, unless you too are alveolar. And even being alveolar doesn’t necessarily make you immune to headaches when you attend a lengthy alveolus.