I remember seeing one directory style website a while ago that advertised itself as having over a million hits a month and for a small (although not inconsiderable!) fee you could advertise on their homepage. Sounds fantastic? Actually no.... hits are very different to visits although many people use the two terms interchangeably.
What is a hit?
A hit is more of a technical statistic that gives a very rough indication of overall traffic. When you open a web page every element on the page has to be downloaded from a web server - each download counts as one hit. If you have a simple text based web page then this counts as 1 hit. If however you have an image on the page then there are two hits when that page is downloaded - one for the text file and another for the image.
Complex pages with multiple images, external program files or style sheets etc can often result in a large number of hits when you download a single page. Going back to our example of the site with a million hits per month - the home page actually contained over 100 images and other external elements - each counting as a hit. This meant that in terms of the number of people actually visiting the site each month we are looking at at least 100 times less - ie probably much less than 10,000 a month. Not terrible but certainly not as great as you might initially believe!
What are visits?
To a certain extent the definition of a visit depends on the web analytics package you are using. A visit is a request for a web page by a "user agent" - this typically being a person! If the person then goes on to view other pages on the same site then this still counts as a single visit. If however the visitor looks at your site for 20 minutes (1 visit) and then returns a few days later this will count as a new visit.
Essentially web analytics packages have a 'time out' period. If a visitor closes their browser or doesn't look at any pages on your site for e.g. 1 hour (if that's the time out period used) and then returns this will count as a new visit.
Google defines a visit as "A period of interaction between a visitor's browser and a particular website, ending when the browser is closed or shut down, or when the user has been inactive on that site for a specified period of time. For the purpose of Google Analytics reports, a session is considered to have ended if the user has been inactive on the site for 30 minutes".
Going back to our scenario above the number of visits per month would provide a far more helpful (and honest!) statistic in helping an advertiser decide whether or not to go ahead and advertise on a particular site. Visitor numbers do not however show the unique number of individual people that look at a site each month.
Absolute Unique Visitors
If you want to know how many unique visitors you have had each month then this is the statistic for you. The number of Absolute Unique Visitors for a given period will be the number of visitors to your site with each visitor counted only once. This figure typically uses cookies (a small text file that gets downloaded) - bear in mind that some people clear out cookies from time to time and others have these disabled. This means that this figure is not entirely infallible but it is the most accurate available.
Should I track Visitors or Absolute Unique Visitors?
That depends on what your business model is. Customer loyalty is important and so having repeat visitors to your site can be just as important as getting new people to find your site. Many organisations choose to track visitor numbers and then rather than Absolute Unique Visitors instead track the % of repeat visitors each month.
