A video signal where some or all of the individual components that make the signal are sent down separate wires (as opposed to composite video), either in the form of a multi-pin D-Sub type cable or a five way cable terminating to five BNC connectors (there are other types, but these two cover the majority of it). For example, in a computer monitor you may find that the three primary video colors (Red, Green, and Blue) are each sent separately, and luminance (brightness) information and video sync are separate from that, hence the five wires (it can even be separate further into horizontal and vertical video sync). In some applications “component” signals are still composite signals of another kind. Formats such as the 4-pin S-Video, the 2-RCA luma/chroma standard, or the 3-BNC YUV standard will have some combining of information, such as the sync signal(s).
Regardless of the kind of cable used, modern analog computer displays have separate signal and ground wires for at least the red, green, blue, HSync and VSync signals. This separation allows the cables to carry much higher frequencies than would be possible if they were entirely or partially composited with each other. These higher frequencies allow for the high resolutions that computer displays must support. For comparison, a computer outputting a 640 x 480 resolution image with a 60 Hz interlaced refresh rate (similar to broadcast TV) has a “dot-clock” frequency of approximately 12 MHz. (Dot-clock represents the timing between adjacent screen pixels and is the highest frequency component of any computer’s display-generation circuitry.) At 800 x 600 resolution (also 60 Hz interlaced), that dot-clock frequency increases to approximately 35 MHz. A modern workstation’s display using 1600 x 1200 resolution at 85 Hz non-interlaced requires a dot-clock frequency of at least 220MHz.
(Special thanks to inSync reader David Charlap for some of the computer specific information presented here.)