courts are typically constructed using wooden floor panels topped with acrylic which are installed over the venue's standard floor. This is the system used for modern indoor professional events such as the ATP Finals. Clay courts can be installed indoors with subsurface watering systems to keep the clay from drying out, and have been used for Davis Cup matches. Carpet courts were once the most prominent of indoor surfaces, especially in temporary venues, but have largely been replaced by removable hard courts. They were used on both the ATP World Tour and World Championship Tennis circuits, though no events currently use them. Historically, other surfaces have been used indoors such as wood courts at the defunct World Covered Court Championships and London Indoor Professional Championships. The conclusion of the Wimbledon Championships, in 2012, was played on the lawn of Centre Court under the closed roof and artificial lights; the Halle Open has also seen a number of matches played on its grass court in the Gerry Weber Stadion with the roof closed. These, however, are outdoor venues with retractable roofs. Terminology Common tennis court terms: Advantage service box or ad court: The receiver's left side service box, or the opponent's right for the server; significant as the receiving side for an advantage point. Alley or Tramlines: The lanes on each side of the singles court. These are only used when playing doubles. Back court: The area between the baseline and the service line. Baseline: The rearmost line of the court, furthest from and parallel to the net. Center service line: The line dividing the two service boxes on each side. Center mark: The 4-inch mark at the halfway point of the baseline used to distinguish the two halves (and service boxes) of a tennis court. Deuce service box or deuce court: The receiver's right side service box, or the opponent's left for the server, significant as the receiving side for a deuce point. Service box: The area on each side bounded by the singles sideline, the service line, and the net. There are left and right service boxes, separated by the center service line. Service line: The line that is parallel to the net and is located between the baseline and the net. It marks the end of the service boxes. Side T: The T shape formed by the service line and the singles sideline. There are four such side