H.100 /H.110
TDM based Computer Telephony (CT) interfaces defined by ECTF, ofter also referred to as CT bus, involving dedicated lines for CLK, FrameSync, and data.
HP
horizontal width dimension (5.08mm)
HPC
FMC allows for two sizes of connector, Low Pin Count (LPC) and High Pin Count (HPC), each offering different (maximum) levels of connectivity. (Wikipedia, FPGA Mezzanine Card)
HPI
Hardware Platform Interface
HPM
Hardware Platform Management
Hz
Hertz