Unreported Missing or 'Missing, Missing' means that the lost person is not officially listed as missing with any law enforcement agency or listed with the FBI's National Crime Information Center (NCIC) database of missing persons, which lists approximately 85,000 names currently.  The following describe various scenarios in which someone may become a 'missing, missing' person. 

The lost/missing person may be estranged from family or friends and no "missing persons" report was requested
Law enforcement may not take an official "missing persons" report in some situations
The lost/missing person may be in this country illegally and undocumented so there may be no official record of his/her disappearance
The person may be an unknown dependent child of an unreported missing adult or teen (for example, a child born to a homeless woman on the streets)