[AZ-AlphaXi]

Here's what the document linked above says (I've bolded the minus list)

Importance of Flex Lists
Flex lists are used only on campuses that use the priority system. A flex list is actually two lists of PNMs — a plus list and a minus list. These lists are used to help optimize the invitations issued by all sororities. Flex lists are powerful tools that enable the RFM specialist to ensure that the number of PNMs returning to each chapter’s events most closely approximate the return number being targeted for that chapter, based on the number of PNMs a chapter needs to have for a successful recruitment conclusion. The RFM specialist draws from a plus list if a chapter does not perform as well as expected. Similarly, the RFM specialist draws from the minus list if a chapter’s performance exceeds projected expectations. Chapters that receive a minus list request from the RFM specialist are required to submit a minus list.