I would call professionals those players who play poker excellently. This requires not only luck but also certain mathematical and analytical knowledge. This way of thinking helps people to make the right analysis, be attentive, and control their behavior in the game, and, as a rule, accumulate experience and skill that will help them win more often. I do not think that you can call professionals those who play slots, where the game itself is based on luck. However, the ability to competently manage your bankroll is also characteristic of those who know when to stop and do not fall into the position of a victim.