A beginner I would say is someone who only started playing chess more seriously no longer than three months ago. Their rating isn't usually anything higher than 1500.
Intermediate players have often played for quite some time and are already quite apt with opening theory, time controls and setting traps. Some 1800-2100 this group is.
Pro players, very simple, are the titled players. GM's and IM's, FM's also probably. CM's is a fifty-fifty whether you include them or not. They have over-the-board ratings of 2200 and higher and online usually at least 2350.
When, are you considered a beginner chess player, intermediate and pro player. What will the ratings be for the 3 groups?