Overlay
There are several types of overlays in the computer world. One type is a video overlay, which is a technique to display video on a computer monitor without having to go through the computer processor. This type of overlay is commonly used by TV tuner cards and early 3D graphics cards.
Another type of overlay is a hardware overlay, which is actually also a type of video overlay. This type of overlay uses dedicated memory inside the video card to render an image to a computer monitor. This process helps to improve the video quality for a computer game, a DVD or a TV tuner card. Most video cards since 1998 support hardware overlay.
A third type of overlay is an overlay network, which is basically a computer network on top of another network. This is used quite commonly today in private networks to improve routing of data. It is also used on the Internet to allow data to be routed to destinations that are not specified by an IP address. This would normally not be possible without an overlay network.
Also see: Network definitions, Video definitions