History
The phrase "grand slam" originated in contract bridge, where it refers to the feat of taking all 13 tricks in a hand.
It was first applied to golf in 1930, when Bobby Jones won what were then the world's four major tournaments: The U. S. and British Open and Amateur championships.
The phrase moved into tennis in 1938, when Don Budge won the Australian, French, U. S., and Wimbledon championships. His accomplishment was widely compared to Jones' feat of 1930.
In tennis, there are three possible grand slams: Singles, doubles, and mixed doubles.
"Grand slam" didn't enter baseball lingo until 1940. In baseball, of course, it refers to a home run with the bases loaded.
The baseball use dominated until 1960, when Arnold Palmer won the Masters and U. S. Open. With the PGA Championship and British Open still to be played, sportswriters decided that Palmer had a chance to win the "new" grand slam. Those four tournaments have since been referred to as the Grand Slam events.
The grand slam in women's golf has not been so well-defined through the years. From 1955 through 1966, the U. S. Women's Open, LPGA Championship, Western Women's Open, and Titleholders Championship were considered major events.
The Titleholders was discontinued after 1966, though it made a one-year comeback in 1972, and the Western was discontinued after 1967, leaving only two major women's tournaments. The Peter Jackson Classic, now the du Maurier Classic, was added to the list in 1979 and the Dinah Shore, now the Nabisco, became the LPGA's fourth major event when it was inaugurated in 1984.
The du Maurier Classic was discontinued in 2001 and it was replaced as a designated major by the Women's British Open.
As in men's golf, the U. S. and British amateur championships are also sometimes considered major or "Grand Slam" events.