Hits represent the total number of requests made to the server during the given time period (month, day, hour etc..).
Files represent the total number of hits (requests) that actually resulted in something being sent back to the user. Not all hits will send data, such as 404-Not Found requests and requests for pages that are already in the browsers cache. Tip: By looking at the difference between hits and files, you can get a rough indication of repeat visitors, as the greater the difference between the two, the more people are requesting pages they already have cached (have viewed already).
Sites is the number of unique IP addresses/hostnames that made requests to the server. Care should be taken when using this metric for anything other than that. Many users can appear to come from a single site and they can also appear to come from many IP addresses, so it should be used simply as a rough guide as to the number of visitors to your server.
Visits occur when some remote site makes a request for a page on your server for the first time. As long as the same site keeps making requests within a given timeout period, they will all be considered part of the same Visit. If the site makes a request to your server, and the length of time since the last request is greater than the specified timeout period (default is 30 minutes), a new Visit is started and counted, and the sequence repeats. Since only pages will trigger a visit, remote sites that link to graphic and other non-page URLs will not be counted in the Visit totals, reducing the number of false visits.
Pages are those URLs that would be considered the actual page being requested and not all of the individual items that make it up (such as graphics and audio clips). Some people call this metric page views or page impressions and defaults to any URL that has an extension of .htm, .html or .cgi.
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