Meaning

noun (usually plural) close-fitting trousers of heavy denim for manual work or casual wear

noun a coarse durable twill-weave cotton fabric

originFrom Gene(s) (also spelled Jean(s)), an obsolete English name for the Italian city of Genoa. Compare French Gênes. In the context of clothing, the term originally denoted a kind of coarse cotton (known more fully as Gene(s) fustian) that was associated with Genoa. It began to be used for trousers made of such cloth in the 19th century. At this point, the final -s was reanalysed as a plural ending.

Etymology from Wiktionary, CC BY-SA 3.0