An introductory college course is usually labeled "Physics 101" or "Economics 101", etc. It is the first course required before you can take more advanced Physics or Economics courses, which might then be labeled "Physics 102" or "Physics 201."
College graduates tend to carry this nomenclature over to civilian life. For example if someone is rude to you

, you might say "Did you take Politeness 101?" - this would mean that the person knows nothing about being polite because he hasn't learned the compulsory prerequisite.