A person at a computer using a browser to visit a web site. A visitor may make more than one visit during a given time period. Note the combination of person, computer, and browser. Since a person may use different computers or even use different browsers on the same computer, it is possible for him/her to appear as more than one visitor because the chief means of distinguishing a visitor is through a persistent cookie or, less desirably, the combination of Internet Protocol address and platform/browser details.