I prefer to think of trading as a home based business rather than a hobby. My hobbies cost me money.
As for a professional trader, that is someone trading for someone else.
I'm from a family of traders. My old man was a successful floor trader for many years until the stress got to him and then he moved on to the FED. I have two relatives that are institutional traders and a few close friends (U.S., Canada and France) that are institutional traders. I obvious consider any trader that works on salary for a firm or getting paid to trade someone's else capital...these are professional traders.
In contrast, traders that work for themselves (their own capital) and its their primary source of income...I consider these types as professional traders too depending upon their associations and if they treat their trading like a business regardless if they do such in a at home office or renting an office space in a building.
Everybody else that either don't treat their trading like a business, its not their primary source of income, their spouse is financially taking care of the family (spouse doesn't consider what you do as a job) or their government doesn't recognize their trading as a job...these are not professional traders. These are either hobby traders or academic traders.
How do you classify the type of trader I am?
My income comes almost exclusively from equities.
Capital gains and dividends.
Both are taxed favorably in Canada.
I certainly don't think of myself as a Professional Trader.
If your primary source of income are via trading...there must be something else going on for you to think you're not a professional trader.
1) Trading is your primary source of income but its not enough to trade for a living. Thus, you're either supporting yourself via a large income earned prior to becoming a trader, you're retired, large inheritance for you to live on for the rest of your life or someone else is supporting you to ensure you have private insurance to take care of you that's not covered by the provincial social health care.
2) You don't treat your trading as if its a business or those around you (family & friends) don't see it as a job for you.
What I'm saying is that there are different variables for someone to label someone as a professional trader and we can't slap that label on someone until we know more information about them.
P.S. Depending upon what country you reside in, citizen of...different rules for considering something as a business from country to another country.