Program Status is the status a lead is in within a program. An example for an lead would be in a trade show or any event type program. This would have a program status of "Invited" or Registered.
A single lead can have multiple program statuses, one for each program membership they have.
A great way to look at it is, I have a Monthly membership to the Gym and a premium membership to the local warehouse club. I have multiple memberships and statuses for those memberships.. However my "Person Status" is different, I am for example licensed to drive in the state I live. My status is either licensed or not..