A shadow box is a type of enclosed diorama, typically used to display or honor life events of a person living or dead. They can contain photographs, personal effects, models, or other representations of the person so honored.
Shadow boxes are separate from plaques or other similar wall-mounted mementos in that they are intended to encase and to some extent preserve artifacts for display in order to specifically associate them with a person.
A military shadow box is typically presented to a person during separation or retirement, and will often include copies of their medals, rank insignia, and other mementos of the person's service.