A grass court is one of the four different types of tennis court on which the sport of tennis, originally known as "lawn tennis", is played. Grass courts are made of grasses in different compositions depending on the tournament. Although grass courts are more traditional than other types of tennis courts, maintenance costs of grass courts are higher than those of hard courts and clay courts. Grass courts (in the absence of suitable covers) must be left for the day if rain appears, as the grass becomes very slippery when wet.