Definition
The term "half-staff" refers to the position of a flag when it is halfway between the top and bottom of the staff. It is often synonymous with "half-mast", although it is argued that this term should only be used if the flag is displayed on a ship or nautical flagpole. The measurement does not have to be exact, but it should be at least the width of your flag. This is to imply that something is missing above the flag. Many scholars refer to this space as the "invisible flag of death," (Martucci).
Symbolic Meaning
Flying a flag at half-staff or half-mast is a sign for grief and mourning. It is flown following the death of certain government officials, in times of national distress, on various holidays, and at any other time it is instructed by the president or government. There are specific instructions in the Flag Code for lowering the flag and the time frame it should be flown. This information is available in the Flag Code section below.
Origin
The practice of half-staffing or half-masting a flag has been taking place for some time. No one knows when and why this tradition began, but the earliest recorded incident was in 1612. It took place after the commander of the ship Heart’s Ease was killed by a native Inuit while searching for the Northwest Passage between the Atlantic and Pacific oceans. His crew flew their flag at half-mast in mourning. When the ship reconvened with its fleet, the gesture was immediately recognized by crew members, insinuating that half-masting was already common practice at that time.
Flag Code
Procedure:
*It is also appropriate to fly your flag at half-staff on:
In Mourning:
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U.S. Code, Title 4, Chapter 1, Section 7.
Half-staff or half-mast? by David Martuccio Flagwire 2006.
The Care and Display of the American Flag by the Editors of SharpMan.com 2004.

