Access Enforcer Role Import - Reaffirm period

Hello

What does the following terms mean;

last reaffirm

reaffirmperiod

We current upload roles into AE, with last reaffirm as current date, and reaffirmperiod of 60 which means 5 years.

Can someone please explain what these terms mean, because many roles have reaffirm periods that end in 2010.

Thanks