The Free On-line Dictionary of Computing (30 December 2018):

scan path

   (circuit design) A technique used to increase the
   controllability and observability of a logic circuit by
   incorporating "scan registers" into the circuit.  Normally
   these act like flip-flops 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)