On the site www.statcounter.com they give lots of information about the meaning of special information they generate. An example with some keywords:
Returning Visitors - Based purely on a cookie, if this person is returning to your website for another visit an hour or more later
First Time Visitors - Based purely on a cookie, if this person has no cookie then this is considered their first time at your website.
Unique Visitor - Based purely on a cookie, this is the total of the returning visitors and first time visitors - all your visitors.
Page Load - The number of times your page has been visited.
What can the Summary Stats tell me?
There are two dimensions to the stats for a 'Standard StatCounter project'. There are the 'Summary Stats', and the 'Detailed Log Analysis'. The 'Summary Stats' provide a lifetime daily count of the totals of visitors to your website each day. And allows you to run reports since the day you started the project! After a few months of tracking, it is absolutely superb to look back and to see the daily, weekly and monthly trends of your visitors. Does your website have a weekday rush and a weekend slump? Did your traffic take a surge leading up to a holiday season? Is your website in general growing or stagnating? It is a wonderful tool to quickly assess the current success of your website.
How do the Summary Stats work?
The 'Summary Stats' determines whether a visitor has been to your website before by using a cookie. So if a user has cookies disabled we have no way of knowing if they are unique or not, and will by default be considered unique. However the majority of visitors have cookies enabled.
To make up for relying on cookies in the summary stats, the rest of the stats are based on your detailed log analysis of the last xxx number of pageloads. The uniqueness in this case is based on your visitors' IP addresses. This method works very well for the majority, but yet again there is an exception. AOL users, and visitors who use what is known as a 'dynamic web proxy' that changes each time they access a webpage. So if a single AOL user visits 7 webpages on your website it will likely come up as 7 different IP addresses!
Both cookies and IP addresses have their strengths and weaknesses for determining the uniqueness of a visitor. It is impossible to be 100% accurate the entire time, but with the Standard StatCounter Project you get the best of both worlds. Cookies for the 'Summary Stats' and IP addresses for the 'Detailed Log Analysis'!
The Advanced StatCounter Project combines the best of both worlds to use an almost fool-proof system (the only problem is AOL visitors who have cookies disabled! Not many!) but it is very server intensive, and won't be possible to provide as a free service until the cost of hardware and dedicated servers come down in price.