Pneumonia vs. bronchitis

What (in layman’s terms) is the difference between pneumonia and bronchitis? Is it possible to have both at the same time?

I am definitely a layperson and not a doctor. However: Pneumonia involves the little bitty air sacs deep in the lungs, where the actual oxygen exchange takes place. Bronchitis involves the bronchial passages, which are the tubes leading from your throat into your lungs. The former is much more serious, since if those little sacs get too filled with liquid you can’t get oxygen out of them at all.

Right. Moreover, any -itis is an inflamation or irritation. Bronchitis typically involves infection, but I think technically any irritation of the bronchii is bronchitis, for example by irritating chemicals. Not sure if pneumonia means infection or perhaps filling with liquid or what, but I don’t think it necessarily implies irritation.