1. Often such organizations have a firewall to protect their internal network against intruders. This means, that their network is logically separated from the rest of the Internet and that they have to use such a proxy server, which is able to communicate with the inside and the outside of their local network.
2. To reduce network load somewhat, the proxy server acts as a local copy machine: As soon as a page is loaded into a browser through such a proxy server, the proxy saves a copy of this page in it's disk cache much like a browser does in the scenario above. This way, documents requested very often by users in the same local network need to be transferred to the proxy only once, which then answers future requests for the same page from it's local cache instead of connecting to the original web server the document originated from.

Definition of Terms

Term	Color	Meaning
Hits		A hit is any response from the server on behalf of a request sent from a browser. This includes any response from the server, not only text files or documents. If, for example, a HTML page has two images embedded, the server generates three hits if this page is requested: one hit for the HTML page itself and two hits for the two inline images.
Files		If the user requests a document and the server successfully sends back a file for this request, this is counted as a Code 200 (OK) response. Any such response is counted for as a file. Again, "file" here means any kind of a file.
Code 304		A Code 304 (Not Modified) response is generated by the server if a document hasn't been updated since the last time it was requested by the user and therefore there was no need to actually send the files for this document. This happens if the browser (or a caching proxy server between the browser and your web server) still has an up-to-date copy of the page in it's local storage (cache) and therefore can display the page without requesting the actual content. This technique is used to reduce network traffic, but it also causes an inaccuracy in the statistics reports regarding the number of visitors, because the browser or proxy usually sends only one such a conditional request per user session if it still holds an up-to-date copy of the file. However, the ratio between files and 304's reflects the efficiency of overall caching mechanisms for at least those hits which made it's way to the server.
Pageviews		Pageviews are all files which either have a text file suffix (.html, .text) or which are directory index files. This number allows to estimate the number of "real" documents transmitted by your server. If defined correctly, the analyzer rates text files (documents) as pageviews. Those pageviews do not include images, CGI scripts, Java applets or any other HTML objects except all files ending with one of the pre-defined pageview suffixes, such as .html or .text.
Other responses	¹	There are much more responses than only Code 200 (OK) and Code 304 (Not Modified) responses, especially in the coming standard, the HTTP 1.1 protocol specification. For example, the server could generate a Code 302 (Redirected) response if a page has moved, a Code 401 (Unauthorized Request) response if access to the document is denied or a Code 404 (Not Found) response if the requested page does not exist on this server.
KBytes transferred		This is the amount of data sent during the whole summary period as reported by the server. Note that some servers log the size of a document instead of the actual number of bytes transferred. While in most cases this is the same, if a user interrupts the transmission by pressing the browser's stop button before the page has been received completely, some servers (for example all Netscape web servers) do not log the amount of data transferred but the amount of data which would have been transferred if the user would have completely loaded the page.
KBytes requested	¹	This is the amount of data requested during the whole summary period. http-analyze computes this number by summing up the values of KBytes transferred and KBytes saved by cache (see below).
KBytes saved by cache	¹	The amount of data saved by various caching mechanisms such as in proxy servers or in browsers. This value is computed by multiplying the number of Code 304 (Not Modified) requests per file with the size of the corresponding file. Note: Because http-analyze can determine the size of a file only if the file has been requested at least once in the same summary period, the values for KBytes saved by cache and KBytes requested are just approximations of the real values.
Unique URLs		Unique URLs are the number of all different, valid URLs requested in a given summary period. This shows you the number of all different files requested at least once in the corresponding summary period.
Unique sites		This is the sum of all unique hosts accessing the server during a given time-window . The time-window is hardwired to the length of the current month. This means that if a host accesses your server very often, it gets counted only once during the whole month. Only the sum of the unique hosts per month is listed in the statistics report.
Sessions		Similar to unique sites, this is the number of unique hosts accessing the server during a given time-window. This time-window is one day by default for backward compatibility, but it can be changed with the option -u or the Session directive in the configuration file. For example, if the time-window is two hours, all accesses from a certain host in less than 2 hours after the first access from this host are lumped together into one session. All following accesses more than 2 hours apart from the first access will be counted as a new session. This way you may get an estimated number of how many sessions are started on different sites to access your server.