Composite Video is the most common video signal today and is usually transmitted through yellow RCA connections, and is also typically accompanied by a red and white RCA interface as well (Right and Left Audio respectively). Composite is an analog signal that is usually associated with televisions and can typically be found coming out of VCRs, DVD players, set top boxes (like satellite or cable boxes), video game consoles (like Wii and Xbox) and more.
Composite video is often designated by the CVBS acronym, meaning "Color, Video, Blank and Sync". Composite will also take on different formats depending on which area of the world you live in. If you live in North America or Japan, chances are all of the video content you watch through composite video is NTSC. Europe on the other hand uses PAL. The difference is in how the video image is formed, how the devices handle color coordination, and what resolutions the video is played back on.