The definition differs not only only from one affiliate program to another, but also from one affiliate network to another.
Commission Junction defines active affiliates as "publishers with a 3-month EPC > 0 or who are new to the network and do not yet have a 3-month EPC ranking." There's one big problem with such a definition. The adjective "active" in such an interpretation speaks of the affiliate's network-wide stance, but has little meaning for any individual affiliate program.
Looking at another affiliate network's approach to the same subject, let's turn ShareASale. In their "weekly progress reports" ShareASale merchants see an "Active Affiliates" column. ShareASale clarifies:
The Active Affiliates column represents the number of affiliate partners who generated at least one click for your program on the given day...
That's one way to define an active affiliate -- an affiliate who refers traffic to the merchant's website.
Another way to look at things is through the prism of an active display of the merchant's links on affiliate website(s). So, an active affiliate may also be defined as one who has your links up on his/her website.
Multiple affiliate program managers and merchants adhere to yet another definition. For them an active affiliate is one who regularly generates sales/leads for a merchant/advertiser.
How do you define an active affiliate? After all, when we call to activation we must be clear on what activity we desire. All of the above definitions speak to the value an affiliate may bring to an affiliate program. Are certain types of affiliate activities really less valuable than others?