Each contact is able to be categorized as  "Not Interested" or as a "Member." These categorizations should be used once a contact has expressed a desire to no longer be contacted, or has decided to commit to your organization as a member. 

Marking a contact as one of the two categories will remove the contact from your active follow-up assignments. However, the contact will still appear in your overall analytics as well as the Contacts page (if the "Include Not Interested" or "Include Members" filter is selected).