The dartboard is divided into wedge shaped segments numbered non-sequentially 1 through 20. Each wedge is divided by wires which run to the center of the dartboard. The center, or bullseye, is comprised of two parts. The outer portion, often referred to as the large or outer bull, scores 25 points and is a different colour than the central portion which is often referred to as inner or double bull which counts 50 points.
The wedges are subdivided by two narrow rings. The outer ring (or "doubles ring") counts as double the number indicated for that segment of the board. The second ring located approximately halfway between the outer ring and the bullseye (the "triples or trebles ring") counts as triple the number indicated for that segment of the board.
The organization of wires running to the center and concentrically around the dart board are called the "spider" because of their resemblance to a spider's web.