Before the beginning of the Open era in April 1968, only amateurs were allowed to compete in established tennis tournaments, including the four Grand Slams.
Beginning in 1905 and continuing to the present day, all four majors have been played yearly, with the exception of the two World Wars, 1986 for the Australian Open, and 2020 for Wimbledon.
A player who wins all four current major tournaments in the same calendar year, as an individual or as part of a doubles team, is said to have achieved the "Grand Slam".
Winning the four majors and a gold medal in tennis at the Summer Olympics has been called a "Golden Slam" since 1988.
The current Grand Slams are the four most prestigious tournaments in the world held every year, they are distinguished by participation from almost every top player and by their two-week duration, 128-player draw in women's singles.
It's extremely rare for a player to win all four tournaments, "the Grand Slam", in one calendar year.
This was only achieved three times since 1888 by Maureen Connolly, Margaret Court, and Steffi Graf, the latter of whom stands alone in winning the "Golden Slam".
Most statistics are based on the data at the WTA Tour and International Tennis Federation, the official websites of each respective Grand Slam tournament and published sources though this is not a definitive list due to the time periods involved.