The most popular colour I'd never heard of.
A cross between grey and brown. By default, taupe tends to be fairly dark, perhaps akin to a rich gunmetal grey, although there are dozens of variations, including Crayola's version, which is fairly light, what I would generally refer to as tan. It is also available tinted, often rather strongly, with every other color of the rainbow, giving a range of earthy colors.
If you would like to be technical, The Oxford dictionary claims that it is specifically 'grey tinged, especially with brown'. But this is the only dictionary I've seen with this definition, and if you see any product in your local store that calls itself 'taupe', it will be grey-brown. For what it's worth, my Webster's Third International Dictionary cross-references taupe to mole grey, which it defines as a slightly greenish blue-grey. This same dictionary also lists the colours Taupe brown, Taupe Gray, and Rose Taupe, all variations on the basic theme.
Pronounced 'Tope'. It comes from the French taupe, of the same meaning, but more interestingly, it originates from the Latin talpa, referring to a mole (the small, burrowing animal).
This site describes taupe as RGB 204,204,153 / HEX cccc99, and "dark taupe" as RGB 153,153,102, HEX 999966.