101 /ˌwʌn əʊ ˈwʌn $ -oʊ-/ number 1. Psychology 101/Economics 101 etc American EnglishAmE a course that teaches you the most basic things about a subject
2 that’s/it’s Psychology 101/Marketing 101 etc informal used to say that a piece of knowledge relating to something is very simple and basic If you’re with a girl, don’t stare at other girls: that’s Dating 101.