These two properties determine if a relationship is required or not. A value of 0 means that the relationship is optional, whereas a value of 1 means the relationship is required.
A relationship configured with Min1=1 and Min2=0 means that the object at end 2 cannot exist without this relationship being present as it has to be related to at least one object at end 1. For example, SPFMenuItems is configured like this because a menu item cannot exist without being related to a menu.