Any of various colors resembling the color of human blood; the primary color at one extreme end of the visible spectrum, an effect of light with a wavelength
between 610 and 780 nm.
The color red symbolizes 'stop' or 'danger' in Western Culture, green being symbolic of 'go' or 'safe'. In Eastern cultures, red is generally a sign of good fortune - often used in wedding dresses or as a symbol of happiness. As the world turns we're seeing the cultures slowly merge and red wedding dresses are popping up all over California while the Chinese throw white weddings sans Billy Idol (thankfully).
Red is often used as slang for people with red hair ('carrot tops, copper tops') - esp the Irish. In Canada, it further denotes the Canadian 50 dollar bill which is a red colour.
R.E.D. also denotes Random Early Discard. Routers use this instead of tail-drop to improve TCP performance when their queue overflows. As the queue fills, the router begins to randomly discard datagrams.
'Red', finally, is an album by the progressive rock group King Crimson. Released in 1974, it was considered a masterpiece especially considering that David Cross left the band while it was being recorded.