Source : Free On-Line Dictionary of Computing

PNP
     
        1.  A type of {bipolar transistor} consisting of
        a layer of N-doped {semiconductor} (the "base") between two
        P-doped layers (the "collector" and "emitter").  PNP
        transistors are commonly operated with the emitter at {ground}
        and the collector at a negative {voltage}.
     
        In the 1960s, the germanium PNP transistor was the cheapest
        and best for use at ordinary temperatures.  The {leakage
        current} from collector to base in this type of device is
        larger than for the silicon transistor, and also varies more
        with temperature.  The effect of these deficiencies can be
        lessened by proper biasing and feedback, which can make the
        circuit both serviceable and reliable.  Neither germanium nor
        PNP transistors are as common today.
     
        The voltages used on a PNP transistor are inverted when
        compared with {vacuum tubes}.  Further, the behaviour of
        vacuum tubes is usually described in terms of {voltages}
        whereas transistors are better described in terms of
        {current}.
     
        2.  {plug and play}.
     
        (1997-05-05)