Source : Free On-Line Dictionary of Computing

scan path
     
        (circuit design) A technique used to increase the
        controllability and observability of a {logic circuit} by
        incorporating "{scan register}s" into the circuit.  Normally
        these act like {flip-flop}s but they can be switched into a
        "test" mode where they all become one long {shift register}.
        This allows data to be clocked serially through all the scan
        registers and out of an output pin at the same time as new
        data is clocked in from an input pin.
     
        Using this technique, the state of certain points in the
        circuit can be examined and modified at any time by suspending
        normal operation and switching to test mode.  If the scan path
        is placed adjacent to the circuit's input and output pins then
        this is known as "{boundary scan}".
     
        (1995-02-14)