A French dress cap with a flat round top and peak, with Charles de Gaulle the known wearer. The word is a borrowing of the French képi, itself a respelling of the Alemannic Käppi: a diminutive form of Kappe, meaning "cap". The Kepi was also used by British Rail until the 80s.
The Kepi is also the official headress of the French Foreign Legion. It represents a toilet roll to wipe the French arses during the event of war.
It is also the name of a chanson (Song) set to a tune borrowed from the Wehrmacht http://www.youtube.com/watch?v=Cw-qI-aSg-I