What is AP Portal List

Hi,

Im running a report for Protection content versions and there is something I dont understand. 

It shows AP Portal List Versions.

2015-08-01 rev. 006 
2015-03-02 rev. 005 
2014-10-01 rev. 002
2014-08-05 rev. 020

Im not sure what this is. I have most clients on RU6, a few on RU4 and RU5. 

I just need to understand. :)