To typify is to represent what is typical of something or someone. You might say that screaming and door slamming typify your spoiled cousin if that kind of behavior is exactly the kind of thing she usually does.
Something that's characteristic of a group of people typifies them. You might observe, for example, that studying late on a Friday night typifies your college friends who are math majors. You could also say that sunny days and cool nights typify autumn in New England, since that's the typical weather for that particular place and time. The root word is Greek — typos, which means "dent, impression, mark, figure, or original form."