Overlay
There are several types of overlays in the computer world. One type is a video overlay, 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 3-D graphics cards.
Another type of overlay is a hardware overlay, which is also a type of video overlay. These overlays use dedicated memory in 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 (digital versatile disc) or a TV tuner card. Most video cards since 1998 support hardware overlay.
A third type of overlay is an overlay network, a computer network on top of another network. This type of overlay is used with private networks to improve routing. It is also used on the Internet for routing data to a destination that are not specified by an IP address. Normally, this type of routing is not possible without an overlay network.