Variable / URL variable
Refers to information that is passed to the server with the URL that the server uses within the context of a script or server-based program.

Visitor
The term is sometimes confused with unique visitor. The difference is that one unique visitor visiting a site repeatedly over a period of time will show up on the site's log file as many visitors. The term therefore refers to the number of times people visit a site - not the actual number of people visiting a site.