- Hits - this simply refers to the number of 'elements' loaded on your site. If one page has five images in it, viewing that page once adds 6 hits (one page + five images).
- Impressions - the number of times all the pages on your site are seen (also simply called pageviews). Impressions are sometimes referred to as 'hits' which can cause confusion.
- Unique Impressions - the number of people that visited your site.
So to clarify, if I visit your website, look at two pages, and each page has 5 images on it, then your stats increase by one unique, two page views, and 12 hits.
Tracking on your site can be either done server-side or remotely. With server-side statistics, log files are used to generate visitor information.
Another option is Google Analytics, a free third-party web analytics software.