All web-site visitors can be divided into users and robots.
Robots are search bots, various site-checkers etc. Robots are singled out with the help of "Robots" data dictionary. If a visitor's User-Agent record appears in this dictionary, then the visitor is considered as robot, otherwise he is counted as a user.
Visitors are those who doesn't belong to robots. Therefore, data dictionary is the explicit indetifier for defining a visitor as a robot or as a visitor.
Visitors subcategory - users - is singled out upon using "Combined" counter type. These are visitors, which execute java-script counter code and download a blank image.
Upon using "PHP-Include" counter a visitor is considered a new user provided that there had been no pages downloading from this IP-address for more than an hour to the moment of a user request.
Upon using graphic counter types all visitors are defined as users.
Users uniqueness is defined in various ways according to the counter type. When "PHP-Include" is chosen for a counter, then a user (IP-address) considered unique if he didn't download the site pages for more than an hour. In case other counter types is used, then cookie is enabled, which expires at 23.59.59. As long as cookie is enabled, the user is not counted as a new one.
Pageview - downloading of any page of the site with embedded counter code.
Host - IP-address, from which request to the site pages is defined.
There are "Pageviews" and "Hosts" colums in the reports: