Number of unique visitors for the selected period. Visitor is a unique "Cookie", which is assigned to every user. If a user disabled cookies in the browsers a visit will not be counted.
Sessions per visitor
Number of sessions per visitor during the selected period.
Session
A sequence of a visitor page views with no more than 30 minutes between then. If more than 30 minutes passed between page views then this page views belong to different sessions.
Page views
The number of times a page was viewed.
Page depth
Total page views per visitor for the selected period.
