Serena Williams achieved a Surface Slam in 2015 by winning major singles titles on hard, clay, and grass courts.
She opened the 2015 major season by defeating Maria Sharapova in the Australian Open final on hard courts. She then won the French Open on clay, beating Lucie Šafářová, and Wimbledon on grass, defeating Garbiñe Muguruza. Those three victories covered all three surfaces used at the majors.
The term is not one of tennis’s four official Grand Slam labels, so it is sometimes confused with a calendar-year Grand Slam. Williams did not win all four 2015 majors: her run ended in the US Open semifinals against Roberta Vinci. She had already completed a career Grand Slam by winning each major at least once across her career, and a Golden Slam additionally requires an Olympic singles title.
Her 2015 campaign was nevertheless historic. She won three of the four majors, extended her major-title streak to four from the 2014 US Open through Wimbledon 2015, and finished the year ranked No. 1.