HIT COUNTS:
By far the most used number and the least useful: when you request a page each element on the page generate a hit count. If the page contains 10 images (elements) this page request produces 11 hits (10 hits for the images + 1 hit for the page itself). Many web-sites try to capitalize on this hit count by generating as many hits as possible for each page request. As a user you'll see that your browser will make many connections to the server even though you have requested just one page. The downside: you wait longer, and the resulting hit count has little to do with the true number of visitors to the site.

UNIQUE HOSTS:
When you make a request to an Internet server your request is tagged with a "unique host ID". This ID is an IP address (Internet Address) that represents the gateway that you have used to connect with the Internet. This gateway can identify a single computer (the no-sharing case) or it can identify a complete network (the shared-gateway case). Often when you connect to the Internet through AOL or Compuserve or many other large companies (such as Boeing) your connection is represented using a single shared gateway address. Thus, the same gateway ID that you present to the server is also the same ID that many others who share this gateway present (in many cases there are tens of thousands of users sharing the same "unique host ID" making this ID useless in trying to determine how many users actually arrived from this gateway).

VISITOR COUNTS:
Each visitor receives a unique ID no matter which gateway they arrived from or how many users share a given gateway. This is the best and most accurate count of actual users to a web site. It provides a true and accurate visitor count - counting each live person as a single visitor while ignoring the by products of this visit (i.e hit counts, page counts, etc.). An increasing number of sites on the Internet provide this measure (Landings is one of them).