The Rules of Lawn Bowling
Lawn Bowling is an outdoor game in which a ball (known as a bowl) is rolled toward a smaller stationary ball, called a jack. The object is to roll one's bowls so that they come to rest nearer to the jack than those of an opponent. This is sometimes achieved by knocking aside an opponent's bowl or the jack.
Bowls is generally played on a flat lawn, about 40-42 yards square. The green is divided into six rectangular sections, or rinks, each of which is about 18-21 feet wide. The bowls are also called woods, but they may be made of rubber, wood, or some other thing-a-ma-jigger. Bowls measure from 4 3/4 to 5 3/4 inches in diameter and have a maximum weight of 1.5 kg. They are black or brown in color.

They are also flattened on one side, so that they follow a curved course when rolled. The jack is white in color, weighs 0.2 to 0.3 kg, and has a diameter of 2 1/2 inches. Players roll their bowls from a rubber mat of 24 by 14 inches.
To begin play, a jack is rolled to the opposite side of the rink, and it becomes the target so long as it stops at least 25 yards (23 m) from the delivery mat. Players then bowl in turn. In singles and doubles games, each player uses four bowls; in triples, every player has three bowls; and in fours, or rink games, two bowls per player are used. When all of the bowls have been thrown, an end is said to be complete. In scoring, all the bowls of one team nearer the jack at the finish of an end than the nearest bowl of the opposing team count for one point each. A game consists of 21 points in pairs or fours, and 18 points in triples. There is no prescribed number of points in singles matches, but the usual number played is 21.

Source: Encyclopedia Britannica Online