How do you define a person as "professional artist"?

People who are trained by professionals?
People who treat drawing/painting as their profession?
People who have high artistic skill/technique?

I did not have any real official training of art (the only class I took is a still life portrait class in high school),
I do work on art commissions sometimes, as a part-time job and earning a few extra dollars,
My future profession will be art related, but not drawing/painting (3D animation).

And there are people who refered me as "professional" sometimes, or the "wow you are so pro!" comments.
In my own dictionary, I am still far away from being a professional.
So I wonder, what is the title "professional artist" mean to them?
And you?