Short for troglodyte. One of a generally small group of people, not really interested on having friendly social interactions with ones outside their group, or on being a part of a "cool" clique. Sometimes they can get into small fights with social groups of "jocks". Sometimes can feel futher alienated by their own trying not to fit into a popular group, and resent their more popular peers.
The "trogs" generally aren't on good terms with "jocks", or any other groups thought to be better then others.