Denim is a rugged cotton twill textile, in which the weft passes under two or more warp threads. This produces the familiar diagonal ribbing identifiable on the reverse of the fabric, which distinguishes denim from cotton duck. The word comes from the name of a sturdy fabric called serge, originally made in Nîmes, France, by the André family. Originally called serge de Nîmes, the name was soon shortened to denim.
Denim was traditionally colored blue with indigo dye to make blue "jeans", the contemporary use of jean comes from the French word for Genoa, Italy (Gênes), where the first denim trousers were made.