Abbreviation for Professional Graphics Adapter. Sold by IBM at about the same time as EGA and supported a resolution of 640x400 as opposed to EGA's 640x350. Also had a lot of dedicated hardware to shift the graphics processing onto the card rather than the processor.
Cost a fortune and was targetted at CAD applications. The only time I've ever seen one was in a real IBM AT that was used by the head of CDT at my school.