Half-mast

Half-mast or half-staff refers to a flag flying below the summit on a pole. In many countries this is seen as a symbol of respect, mourning, distress, or, in some cases, a salute. Strictly speaking, flags are said to be half-mast if flown from ships and half-staff if on land, although not all regional variations of English use ''half-staff.''

Is this statement correct "can you fly a flag at half mast"?
yes