Horizontal flickering line across the screen

I've been having a problem with my screen for a few weeks now. When I fire up my MBP, grey, black and white lines flicker horizontally and randomly across the screen all of a sudden. Quite often the lines are fairly broad and sometimes are just faded strips of what was being displayed right before the flickering started.

For the moment I can make it stop by shifting the screen again or wiggling it back and forth until the flickering stops. And sometimes it doesn't work out so I have to restart the MBP.

What is wrong with the display?