Tennis has no league table and no fixture list that everyone plays. It has a circuit. Players choose their tournaments, earn points for how far they go, and carry those points for exactly one year before they expire. That single rule shapes everything: a champion who skips a tournament in January is losing ground in January a year later, whether or not they lost a match.
The season runs from the middle of January to the middle of November and moves by surface, not by geography. It opens on hard courts in Australia, spends the spring on European clay, compresses a whole grass season into five weeks around Wimbledon, returns to hard courts for the North American summer and the Asian autumn, and closes indoors.
Below the four majors sit the 1000-level events: nine ATP Masters and ten WTA 1000 tournaments, six of which are played by both tours in the same fortnight at the same venue. They are the events the top players are expected at, and they decide the ranking, because the majors are too few to separate anyone.