The length of time a user/visitor stays actively on your site. Average Active User Session is not the same as Average User Session. Most analytical packages only show the latter. Average Active User Session is calculated by dividing the user session by the number of pages to get the average time spent per page. Every site has an optimal flow state and AAUS is one of the measures that will help you find yours. Remember, AAUS is about the entire site and the overall path of the user whereas when you look at TPP (Time Spent Per Page), you’re typically looking at individual pages.