noun
denim
DEN-im/ˈdenɪm/
Durable cotton cloth woven with diagonal ribs.
The folded denim shows its pale reverse and frayed cotton edge.

Etymology
The pieces mean “from Nîmes,” identifying the town in the phrase “serge from Nîmes.” Originally naming a kind of serge, denim later came to mean the coarse twilled cotton cloth used for jeans.
In context
And what I love about this outfit is how casual but still refined it is because of the tie. He's wearing denim on denim. So he has a pair of jeans and then also a denim shirt underneath.