The most popular colour I'd never heard of.
A cross between grey and light brown. (The Oxford paperback dictionary claims that it is, more 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).
Pronounced 'Tope'. This word has a rather annoying etymology; all the dictionaries agree that it is French, from the Latin talpa, meaning mole. Of course, 'mole' has many meanings. The two most likely definitions of 'mole' are "a stain or discolouring" or the little burrowing mammal.
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.
http://www.csuohio.edu/identity/wcolors.html describes taupe as RGB 204,204,153 / HEX cccc99, and "dark taupe" as RGB 153,153,102, HEX 999966.