x S-Video Connection/sTerm used to describe systems that output or transmit separate "Y" Luma (Black & White) From "C" Chroma (colour) signals
The SCART connection which is used in Europe can carry an S-video signal, although most people associate it with the 4-pin DIN (pictured above) connection that became popular in the 80's on S-VHS video recorders and camcorders.
S-Video is a huge improvement from composite
As to whether RGB or S-Video is better in the average set-up depends on the users equipment (Some TV's don't work all that well with RGB)
Convenience also plays as factor as not many AV amps/receiver on the market have SCART switching, but most have S-Video switching (Can be an issue if you have a lot of video sources to wire up to a TV with just 2 or 3 SCARTS)