All accesses to a web site can be logged by the web server. Data that is usually logged includes date and time, filename accessed, user's IP address, referring web page, user's browser software and version, and cookie data.
A file that lists actions that have occurred. For example, Web servers maintain log files listing every request made to the server. With log file analysis tools, it's possible to get a good idea of where visitors are coming from, how often they return, and how they navigate through a site. Using cookies enables Webmasters to log even more detailed information about how individual users are accessing a site.