It's hard to define "professional" in the art/creative/theatrical worlds.
I take a relatively hazy stance myself. It probably goes something like this - if your only source of income or at least 50% of your income is from your own creativity then you're probably a professional artist (of whatever persuasion).
Then there are those of us who have day jobs which generally pay the bills and allow the occasional evening out without too much wincing at the bank balance. Some of us have reached a decent standard in our chosen artistic/creative field; in my case I flatter myself that I'm not a bad actor, I'm a decent front-man and I can hold a tune when I sing.
I think it's reasonable to think of this as being, perhaps semi-professional. I'm perfectly happy to work without payment in a community project for which I can see the benefit to all and sundry. I don't however perform or otherwise work as matter of course without a few pennies being proffered and agreed upon. Before anyone says anything - the morris is my hobby and the standard of my guitar playing means I should probably pay them for having me along.
I rather liked this photo which my lovely niece (a working professional actor), Georgina posted on her Facebook wall.
I think some of us need tee-shirts with this on....