These are my own definitions. Other missing persons organizations/websites may have different ideas of what these mean.

Missing

The default classification for adults under 65.

Endangered Missing

The default classification for minors (under 18) and elderly persons (over 65). An adult between those ages will be listed as Endangered Missing if they have a medical condition or are missing under circumstances that indicate they may be in danger.

Endangered Runaway

A minor missing under circumstances which indicate that he or she left voluntarily.

Family Abduction

A minor who is believed to have been taken by a family member, such as a parent, who does not have legal custody and/or a legal right to take the child.

Lost/Injured Missing

A person of any age missing under circumstances that strongly indicate they had an accident that caused their disappearance, or that they became lost in a wilderness area. Foul play is not suspected in these cases. Most probable suicides are included; people who wandered away as a result of mental illness or dementia are not included. An example of a lost/injured missing person would be someone who disappeared on a rafting trip.

Non-Family Abduction

A minor who is believed to have been abducted by a non-family member.