Most of the online dictionaries define commute as a trip between home and work. Of course there are commuter students at colleges also.

But within the cycling community, "commuter" has a more specific sociological definition. Commuters tend to have a certain attitude, and to use identifiable clothing, gear and bikes. In some ways, I am always a commuter--even when I'm watching TV in the evening--because it's a group in which I claim membership. This is similar to saying that I'm always an American, or I'm always a Methodist. And a nudist is a nudist even when he's wearing clothes.