There are 27 (or thereabouts) tour events. Most of them are ranking events (open to a set number of ranked players plus some qualifiers) and a handful are invitational. The tournaments considered majors are the World Championship, the U.K. Championship (both ranking events) and the Masters (an invitational non-ranking event for the current top 16 players, well actually the defending champion and the top 15 otherwise in the rankings). Because of the big prize money it’s quite possible that the China Open and the new Saudi Arabia masters will one day be considered majors alongside the other three.
