Visitors The number of distinct people visiting your site.
Page Views The number of web pages and amount of times they have been viewed by visitors to your site. Each time a visitor, even the same visitor, views a page it is considered a new page view.
Referrer URL The website that a person visits your site from. For instance, this may be a search engine or another site that has a link to your website. Referrer URLs are the sites which are providing you with traffic.