The definition of commute is a bit wider than travel between home and work. It relates to any regular travel between any two places. For instance, if I ride every Tuesday and Thursday evening to and from the local polka emporium then that would be a commute. Houwever, as tsl says I am more proud of the number of days per year I commute on work days. Unfortunately, I am compelled to drive to work 3 times per year: Twice to get my 2 cars inspected and once for a training course in a neighboring city.

I don't count the weekend days I ride to work because they are not work days (I still count the mileage though). Occasionally I will work from home on a work day, but then ride into my office after hours - does that count?

Actually, I have found that stressing about mileage or trips takes some of the fun out of just riding.