Taken from the applecare service source.
Horizontal and Vertical TAB Faults
These are caused by a connection failure from the TAB that connects the transparent electrode layers to the video driver board.
TAB stands for Tape Automated Bonding, which is one of several methods employed in the LCD display manufacturing process to electrically connect hundreds of signal paths going to the rows and columns of electrodes in layer 6 (the transparent electrode layer) in the LCD display to the video ICs on the driver board that drive these electrodes.
If an LCD display is subjected to extreme heat or cold or physical shock, this could cause one or more TAB connections to fail inside the display. This failure requires replacement of the LCD display module itself.
If these connections were to fail, the effect would be that an entire row or column of pixels would fail to activate. In the examples below, a horizontal or vertical black line would appear on the display, while the rest of the display would appear normal. The horizontal failure runs from edge to edge; the vertical failure runs from top to bottom.
Depending on exactly how a tab connection fails, it could cause either a dark line defect or a bright line defect. In the examples below, a horizontal or vertical white or colored line would appear on the display, while the rest of the display would appear dark. As with the above failure, the horizontal failure runs from edge to edge; the vertical failure runs from top to bottom. Either way, the cause remains the same.
Whether the symptom is a white line, a black line, or a colored line, horizontal or vertical, the important thing to remember here is that TAB faults are resolved only by replacing the LCD display module itself, not by flexing the LCD display module, rubbing the display, or some other 'urban myth' method.