In tennis betting, a "grand slam" typically refers to wagering on a player to win all four major tournaments in a single calendar year: the Australian Open, the French Open, Wimbledon, and the US Open. This is a highly ambitious and difficult feat, as achieving a grand slam requires consistent top-level performance across varying surfaces and conditions throughout the year. Betting odds for a player to accomplish this can be quite long, reflecting the rarity of such an achievement in the sport.