If today's date is after a member's expiration date, then the member will be considered Expired unless the member is subject to your Grace Period. Your business rules might call for expired members to be converted to Prospects at some point in time.
Prospects are records that have a member type but have no "Member Since" or "Membership Expires" dates. They are also not entitled to member benefits.
In Novi, this is a semi-automated process that can be done on the record level.
Warning: Converting a record to a Prospect removes the membership since and expiration dates, which will affect reporting and historical data.
To convert a member record to a prospect:
Navigate to the Details tab on the member's record.
Delete the dates in all 3 date fields:
Original Join Date
Current Membership Since
Membership Expires
Then click the Save button.