Wayback Machine - technical definition

A Web site from the Internet Archive (www.archive.org) that records the content of most Web sites for each year of their existence since 1996. All of the pages in the site are generally included unless the site is password protected or is coded to explicitly refuse to be archived (see robots.txt). The Wayback Machine enables users to review past information that is no longer visible. It also provides an evolution of the site's design over the years.