the number of days an affiliate can earn commission on a conversion (sale or lead) by a referred visitor.

The number of days that can elapse between an initial visit by a referred customer and a return visit in which that customer makes a purchase or takes an action. When you create a program level or promotion, you are asked to indicate the number of return days that you will accept. If customers make a purchase or take an action within the number of return days you indicate, the referring affiliate will still be compensated, even if customers don't return from the affiliate's site.

The number of days between a user's first visit to a merchant's Web site and their next visit.