1
general::
Phrase(s): at half-mast [and] at half-staff
[of a flag] halfway up or down its flagpole. • The flag was flying at half-mast because the general had died. • Americans fly flags at halfstaff on Memorial Day.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Halfway up or down, as in The church bells tolled off and on all day and the flags were at half-mast. This term refers to placing a flag halfway up a ship's mast or flagpole, a practice used as a mark of respect for a person who has died or, at sea, as a distress signal. Occasionally the term is transferred to other objects, as in Tom's pants were at half-mast as he raced around the playground, or The puppy's tail was at half-mast. [First half of 1600s]
American Heritage Idioms