I am honestly asking this question as I deal with new graduates each year. Just because someone has received a degree from a university does not mean that they are now suddenly “professional.” That term must be earned through experience and practice. Just because you know how to play an instrument for pay does not make you a professional musician. There is a difference between being a paid musician and being a professional musician.
A professional musician is one who has taken the time to learn the ropes in the real world from his fellow musicians (usually older and more experienced). He has learned how to handle contracts, act on the actual gigs, deal with referrals and business contacts, and most importantly, be a responsible, ethical person.