Total Number of Visits
The Total Number of Visits is a reliable indicator of traffic which uses IP address tracking to identify individual site visitors. This avoids double-counts and gives a slightly conservative figure. It is probably the most accurate figure you will get for traffic.
Total Number of Unique Visitors
Unique Visitors are tracked and recorded in case your strategies are directed towards first time page viewing. It is also useful to know how many of your visitors are making return visits. Cookies (small text files) left on visitor's computers are used to determine if the visitor has been to the site in the past (defined as the previous 12 months). This is not a particularly reliable statistic as many people "refuse" cookies for security reasons and the use of corporate gateways and shared IP addresses makes IP tracking unreliable. But this is as good a measure of "repeaters" as you will ever get.
Total Number of Requests
The Total Number of Requests is calculated to give a comparative measure of "hits" as recorded by the more primitive hit counters which are still in use on many websites. A single visitor viewing a page with 6 images on it would be recorded as 7 hits, and after viewing a second page with 5 images, a total of 13 hits would have been racked up. The HitList Log Analysis software, by contrast, would know that this is the same visitor (by IP tracking) and would simply record it as one visit.
Whenever a surprisingly high number of "hits" is claimed for a website you will usuall find that it is Object Requests that are being measured.