Craig Newmark notes a Slate Explainer that tries to answer the question, “why are introductory college courses numbered ‘101’?”

Oddly enough, of all the institutions I’ve taught at, only Ole Miss numbered a political science course (in that case, Intro to American Government) as 101. At Millsaps, the same course was 1000; Duke was 91 (or 91D if taught with discussion sections); and here at SLU it’s 110 (we have a “100” but no “101”). Not only that, but all four institutions also use different abbreviations for political science—POL, PLSC, POLSCI (or unofficially PS), and POLS, respectively.