Here is the wiki page http://en.wikipedia.org/wiki/Video_In_Video_Out
Video In Video Out, usually seen as the acronym VIVO, enables video cards to have bidirectional (input and output) video transfer through one connector, by using a specialised splitter cable. VIVO is commonly pronounced "Vee-Voe", but other pronunciations are in use.
VIVO is featured on some video cards, such as the Nvidia GeForce range and the ATI Radeon series. It can receive input from RCA or S-Video sources, and typically moves output over RCA, less commonly over S-Video. However, at this time, S-Video is more widely used for VIVO by both Nvidia and ATI.
Some VIVO cables also support the output of component luminance, and 2x chrominance, enabling HDTV support. However as this connection is not digital it does not support HDCP which would be required for official HDTV support as set out by the EICTA.