Overscan refers to the portion of the video signal that extends beyond the visible display area of a CRT monitor or television. On the Amiga, the custom chipset (Denise in OCS/ECS, Lisa in AGA) could display graphics in these border areas that would normally be hidden by the screen bezel, allowing programmers to utilize the full potential of PAL or NTSC signals. This capability was extensively used in demos and games to create full-screen effects without black borders, though visibility varied depending on the display device.