Continuing his linguistic studies, Tolkien joined the faculty of the University of Leeds in 1920 and a few years later became a professor at Oxford Universit.
It's when someone makes a fast and false conclusion because they only know the general idea of the thing they are concluding, and not all of the facts, if that makes sense. It's kind of like a stereotype, automatically assuming that someone is a certain way just because they participate in a certain sport, for example.
