Pronounced 'Hippie', the acronym is sometimes also written as 'HIPPI'. It means Hight Performace Parallel Interface. It's a point-to-point, circuit-switched (as opposed to packet-switched) connection technology for short runs between servers, routers and anything else that requires a dedicated, high-speed link.
The ANSI standard X3T9/88-127 which defines HPPI sets its speed at 800 Mbits/s or 1.6 Gbits/s in either simplex or full-duplex.