What’s the difference between hits, impressions and unique visitors?

Hits – these are number of objects that have been transferred to your visitor’s web browser. So if your page has 10 images on and it is downloaded once then you will have received 11 hits (1 HTML page + 10 images).

Impressions/Pageviews – the number of pages that were viewed by your visitors.

Unique Visitors – the number of people that visited your site.

Thus if I visit your site and go to 3 pages, each of which has 5 images on it your stats program will report the following: 18 Hits; 3 Impressions; 1 Unique Visitor.