Contacts: total number of request made to the server in a period of time.
(every single page generates several contacts, one for each linked resource like images, animations, style sheets, etc)

File: total number of requests (contacts) that send data to users.
Not every contact sends data to the user, for example the 404 request (page not found) and the requests for pages that are already loaded on the browser cache in the "File" parameter aren't considered.

Pages total: all the pages viewed by the users that visit your site

Visits total: a visit is the set of pages requested to the server from the same IP during a 30 minutes time span.

KBytes: amount of data transfered from the server to the user's pc.

Host names: number of different IP addresses that made requests to the server.

URL (Uniform Resource Locator): URL is a sequence of characters that identifies the address of a resource (HTML, audio, images, ecc.) on your server.
This parameters takes into account every request for objects (or resources) made to the server of your site.

Referrer: these are the addresses of the pages that contain a link to a page (or to a resource) of your site.
Many requests come from the pages of your site itself, because most of them contain links to objects (like images or files).
For example, if one of your pages contains 10 images, the users that will see your page will score 10 "contacts" and in the referrer section you'll find that page.

Browser: type of browser used to view your site.