Handstamp - A stamp or overprint which has been applied to paper singly and without mechanical means; a hand-held apparatus for printing that is struck on an ink pad and then pressed on paper. The die may be of metal, rubber, or wood.
Heller - 1/100 of the Krone/Florin, the official currency of the Austro-Hungarian Empire from 1892 as part of the adoption of the Gold standard.
Hinged - An unused postage stamp to which a hinge (stamp mount) has been affixed is described as 'lightly hinged' or 'heavily hinged', depending upon the degree of gum disturbance.
HPO - Abbreviation of Head Post Office.