Tennis is unusual among major sports in changing the ground underneath itself several times a year. A basketball player competes on a hardwood floor built to a specification. A tennis player moves between surfaces that differ in construction, and those differences alter the bounce of the ball, the way a foot interacts with the ground, and consequently the kind of tennis that wins.
The differences are usually described in terms of speed, which is a poor summary: speed is a consequence, not a property. What actually varies is how a surface deforms, how much friction it offers and how consistently it behaves, and every tactical difference between grass, clay and hard court follows from those three things.
