The preposition except means "excluding." When we refer to the continental United States, we mean the whole country except Alaska and Hawaii.
This word can also be used as a conjunction meaning "but": If you're not very hungry, you might not eat anything, except a few crackers. As a verb, except is often used in the past tense: All drivers must obey the speed limit, but ambulances rushing to the hospital are excepted. Much more rare is the use of except as a verb meaning "to object," which we find mostly in legal contexts.