The wash of a pair of jeans refers to the faded pattern on the jeans. The term “wash” can be used both as a verb to describe the process of washing (“this pair of jeans was stone washed”) as well as a noun to describe the final effect (“that pair of jeans has a cool wash!”).
Different washes are achieved through different techniques such as stone washing, acid washing, sandblasting, and even bleaching to give a new pair of jeans a more worn look.
It has recently become more fashionable for jeans to have a slightly worn look, rather than appearing brand new. Faded jeans can also appear more rugged (similar to jeans that have tears in them) and are also more interesting and dynamic than a pair of jeans that is monotone.
Getting a pair of jeans with a cool wash is a great if you are going for a rugged hip hop or rocker look. Moderate washes can be a good for many outfits, but don’t overdo it unless you’re peacocking.