Yea as others have mentioned I would class a gambler as professional when
it is their only or main source of income and that they are making a living and or profiting
from that.
Somebody casually gambling would not be classed as a professional gambler IMO.
If only that exists lol.. people still use the word professional nowadays with gambling and it's always very funny to me...The only difference between someone that's a beginner and someone that's a pro is experience...Even those that are experienced cannot make gambling a source of income because it's a game of uncertainty..The only way to make profit is when you win and stop playing permanently