Tennis can be played on a myriad of surface types, though they are generally divided into these three categories.
A court with a grass surface is considered as a "fast" court. It adds an additional element to the game, with variable bounces depending on how healthy the grass is and how recently it has been mowed. Of the major Grand Slam tournaments, the Wimbledon tournament is played on grass court. The Australian Open was until recently played on Grass and the US Open was once played on grass.
Clay courts are considered as "slow", which means the balls bounces relatively high and more slowly, making is difficult for player to hit an un-returnable shot. On clay courts, line calls are easily reviewable because the ball leaves a visible mark. The French Open is played on a Clay court.
The definition of a hardcourt surface encompasses many different surfaces, ranging from old-fashioned concrete courts to coated asphalt to wooden gymnasium surfaces to artificial grass similar to AstroTurf. Hardcourts are also considered as "fast" surfaces, where fast, low bounces keep rallies short, and powerful, hard-serving players have an advantage. The Australian Open and U.S. Open are played on hardcourts - though both originally used grass courts.
Court Surface Speed
The International Tennis Federation (ITF) has a scale for measuring the speed of courts. For example, in the medium to medium-fast pace range is a score of between 34 to 38.