A Site is a remote machine that makes requests to your server, and is based on the remote machines IP Address/Hostname.
URL - Uniform Resource Locator. All requests made to a web server need to request something. A URL is that something, and represents an object somewhere on your server, that is accessable to the remote user, or results in an error (ie: 404 - Not found). URLs can be of any type (HTML, Audio, Graphics, etc...).
Referrers are those URLs that lead a user to your site or caused the browser to request something from your server. The vast majority of requests are made from your own URLs, since most HTML pages contain links to other objects such as graphics files. If one of your HTML pages contains links to 10 graphic images, then each request for the HTML page will produce 10 more hits with the referrer specified as the URL of your own HTML page.
Search Strings are obtained from examining the referrer string and looking for known patterns from various search engines. The search engines and the patterns to look for can be specified by the user within a configuration file. The default will catch most of the major ones.
Note: Only available if that information is contained in the server logs.
User Agents are a fancy name for web browsers. Firefox, Mozilla, Internet Explorer, etc.. are all User Agents, and each reports itself in a unique way to your server. Keep in mind however, that many browsers allow the user to change it's reported name, so you might see some obvious fake names in the listing.
Note: Only available if that information is contained in the server logs.
Entry/Exit pages are those pages that were the first requested in a visit (Entry), and the last requested (Exit). These pages are calculated using the Visits logic above. When a visit is first triggered, the requested page is counted as an Entry page, and whatever the last requested URL was, is counted as an Exit page.
Countries are determined based on the top level domain of the requesting site. This is somewhat questionable however, as there is no longer strong enforcement of domains as there was in the past. A .COM domain may reside in the US, or somewhere else. An .IL domain may actually be in Isreal, however it may also be located in the US or elsewhere. The most common domains seen are .COM (US Commercial), .NET (Network), .ORG (Non-profit Organization) and .EDU (Educational). A large percentage may also be shown as Unresolved/Unknown, as a fairly large percentage of dialup, Wi-Fi and other customer access points do not resolve to a name and are left as an IP address.
Response Codes are defined as part of the HTTP/1.1 protocol. These codes are generated by the web server and indicate the completion status of each request made to it.