The standard course, usually more than 6,000 yd (about 5,500 m) in length, consists of 18 consecutively numbered "holes" (the playing areas leading to the cups). The cup measures 4.5 in. (11.43 cm) in diameter and is set into a smooth surface of closely cropped grass, called a green. Golfers begin play by driving the ball toward the hole from the tee, a slightly elevated rectangular area. Between the tee and the green lies the fairway, often bounded by tall grass (the rough) and trees, and containing natural or constructed obstacles (hazards), such as small lakes or streams, sand pits (bunkers), and mounds. Fairways vary in length from 100 to 650 yd (90–600 m). Two basic principles underlie nearly all the rules: first, players must play the course as they find it and, second, they must play only their own ball, and not touch it (except to hit it with a club) until play is completed on the hole. These principles ensure challenging conditions, demanding skilled shotmaking, and imposing penalties for the loss of one's ball.
The rules have varied little, but changes in equipment have been dramatic over time. In golf's earliest days, the ball was made of feathers stuffed tightly into a leather bag and struck with wooden-shafted clubs. Today balls are of composite materials and can be hit in excess of 300 yds (274 m). A complete set of golf clubs once comprised 3 or 4 woods, used for long drives; 10 irons (numbered upward as the angle of the club face provided increased loft), used for intermediate and short shots; and a putter, used for rolling the ball across the green. Although golfers may carry no more than 14 clubs in their bags, they can now select from 15 different woods, some now made of nonwood materials, from a range of hybrid clubs that combine the characteristics of traditional woods and irons, making them easier to hit than the standard irons they are designed to replace, and from specialized wedges for sand play and for pitching the ball at varying degrees of loft, which complement the standard irons.