A men’s Grand Slam singles match is played as best of five sets, so the winning player must win three sets. A match may therefore finish in three, four, or five sets rather than always lasting five.
The four Grand Slam tournaments are the Australian Open, French Open, Wimbledon, and US Open. Their men’s singles draws traditionally use the best-of-five format, making these matches longer and more physically demanding than most regular tour matches, which are best of three sets.
The phrase “five sets” describes the maximum format, not a guaranteed number of sets. For example, a straight-sets victory has a score such as 6–3, 6–4, 6–2 and ends after three sets. A five-set thriller can require the full format, with one player winning three sets to two.
Women’s Grand Slam singles matches are best of three sets. Grand Slam doubles and mixed doubles can follow different formats, including match tiebreaks in place of a deciding set, so the five-set rule specifically concerns men’s singles.