When someone comes to your site we count a visit(*). After that, there are two possibilities: either that person has never been to your site before or he/she has come at least once in the past (whether a few hours ago or several months ago). In the first case, we speak of first time traffic(*) (it's the first time the visitor ever sees your site), in the second case, we speak of returning or repeat traffic(*).
Note that to recognize repeat visitors we depend on cookies on the visitor's browser. If cookies are not enabled or if they get reset, a repeat visitor will not be recognized by Web-Stat and will be inaccurately identified as a 'first time visitor'. This is a limitations of the system ; unfortunately there is no better way of measuring this metric and all stats providers are subject to the same issue.
Repeat Visits Graph:
The background of this graph shows the total visits on your site. Superimposed in green are the repeat visits (the exact number can be read at the bottom of each bar or by hovering your mouse over the bar)
First Time Visits Graph:
The background of this graph shows the total visits on your site. Superimposed in purple are the first time visits (the exact number can be read at the bottom of each bar or by hovering your mouse over the bar)