Figure skating is a sport in which individuals, duos, or groups perform on figure skates on ice. It was the first winter sport included in the Olympics, in 1908. The four Olympic disciplines are men's singles, ladies' singles, pair skating, and ice dance. Non-Olympic disciplines include synchronized skating, Theater on Ice, and four skating. From novice through senior-level competition, skaters generally perform two programs (short and free skating) which, depending on the discipline, may include spins, jumps, moves in the field, lifts, throw jumps, death spirals, and other elements or moves. The blade has a groove on the bottom creating two distinct edges: inside and outside. Judges prefer that skaters glide on one edge of the blade and not on both at the same time, which is referred to as a flat edge. During a spin, skaters use the "sweet spot" of the blade, formally called a rocker, which is the roundest portion of the blade, just behind the pick and near the middle of the blade. Skates used in single and pair skating have a set of large, jagged teeth called toe picks on the front of the blade. Toe picks are mainly used for the take-off on jumps. Ice dance blades are an inch shorter in the rear and have smaller toe picks. Figure skaters compete at various levels from beginner up to the Olympic level (senior) at local, regional, national, and international competitions. The International Skating Union (ISU) regulates international figure skating judging and competitions. These include the Winter Olympics, the World Championships, the World Junior Championships, the European Championships, the Four Continents Championships, the Grand Prix series (senior and junior), and the ISU Challenger Series. The sport is also associated with show business. Major competitions generally conclude with exhibition galas, in which the top skaters from each discipline perform non-competitive programs. Many skaters, both during and after their competitive careers, also skate in ice shows, which run during the competitive season and the off-season.