What constitutes a "biker"?

I prefer to think it refers to a person that, when presented with the option between driving their automobile or riding their bike, ride their bike. I have 5 cars and 2 bikes. When conditions permit..............I ride instead of drive. After that crash last month I tend to drive my car more in the early morning hours (before daylight). Guess I am a little gun shy still? I go over that same stretch of road every day and I still can't figure exactly where that dog was hiding and why I never saw him until he ran out of the gr.