Motion flow is Sony's name for 120 Hz frame rate with interpolated frames. What that means is
Normal 1080p display shows a complete frame of TV (all 1080 lines) every 1/60 second. (60 Hz frame rate)
Motion flow adds an extra frame to increase the rate to one full frame every 1/120 second (120 Hz frame rate)
There are two possibilities for that extra frame: duplicate the previous frame (easiest) or "interpolate", derive a new frame from information from both previous and next frames to position edges "in between" their locations in those frames. The result is a smoothing of the apparent motion of objects.