Definition - What does PCI Mezzanine Card (PMC) mean?
A PCI mezzanine card (PMC) is a printed circuit board that is used to extend the connectivity or function of a compatible computer system, typically for the VMEbus, Futurebus+ and other computer systems supporting the PCI specification. The PMC standard defines a card or board with the characteristics of the PCI bus as well as the physical dimensions of the common mezzanine card (CMC) format.
Techopedia explains PCI Mezzanine Card (PMC)
A PCI mezzanine card is a peripheral card that extends the functionality of a system by providing a means to connect other peripheral devices and serves as data acquisition cards used in industrial settings for sensors, sonars and the like. These functionalities often yield analog signals, so it is the job of the PMC to receive and transform this data to machine-readable and subsequently to human-readable format. It is basically an extension card providing any functionality that is required.
A PCI card is often slotted perpendicular to the motherboard, but a mezzanine card is slotted in parallel to the motherboard, so a PMC serves as a cross between having the CMC format and sporting PCI connectivity.