see Highway Post Office.

Historic Preservation Officer

Highway Post Office. Portable mail-handling equipment for sorting mail in transit on highways (normally by truck). The last official U.S. HPO ran June 30, 1974.

High Performance Option. An option to improve CICS performance through the use of the VTAM authorized path, which shortens instruction pathlength by not executing certain checking routines (CICS is a trusted user of VTAM).

High Performance Option. See VM/HPO.

Hydrogen peroxide