Pincushion distortion

A common type of distortion in CRT monitors in which horizontal and vertical lines bend inwards toward the center of the display. The distortion is most noticeable at the edges of the display.The opposite of pincushion distortion is barrel distortion, in which horizontal and vertical lines bend outwards toward the edge of the display. A third type of distortion, called trapezoid distortion, occurs when vertical lines are straight but not parallel with each other. Most monitors have pincushion/barrel controls that let you correct these distortions, and many monitors also include a trapezoid distortion control.