A user in Appsee is defined by an every-single installation of your app, and a new user index is allocated only after the 1st app launch.

Definitions:

Active Users = New Users + Returning Users

A New User is a user that had his/her 1st session in the timescope you’re filtered on.

A Returning User is a user that did not have his/her 1st session in the timescope you’re filtered on, but did have session 2 or above.