An LCD is made up of several segments (or complete symbols), which can be visible or invisible. Any single segment has two electrodes, with liquid crystal between them. These electrodes are connected to the common terminal (COM) and the segment terminal (SEG) on the display. When a voltage above a threshold voltage is applied across the liquid crystal, the segment becomes visible. The voltage must alternate, to avoid an electrophoresis effect in the liquid crystal, which degrades the display.