I'm sure when most of us hear the term "commuter" in the context of bike commuters we can conjure up a mental image if asked.

Personally I have multiple images. The first is an image based on what is often thrown out as required commuting accessories: lights, racks, panniers, fenders, bell. Put a rider in hi-viz clothing on top of a bike with those accessories and that's one image of a "commuter". Attach a mirror to the helmet or handlebars for good measure.

The second is based on what I actually see people riding and is more of an amalgam of people and bikes.