Source : Free On-Line Dictionary of Computing

Serial Peripheral Interface
     
         (SPI) A {serial interface} in which
        a master device supplies {clock} pulses to exchanges data
        serially with a slave over two data wires (Master-Slave and
        Slave-Master).  This term probably originated with Motorola in
        about 1979 with their first all-in-one {microcontroller}.
     
        (2003-07-13)