It’s a feature on the leg seam of early vintage or premium jeans, a stripe of white revealed only when the hem is cuffed.
Selvedge — also called selvage or self-edge — is the vertical edge of the denim fabric that prevents the end of the denim from unraveling (without any straight or overlocking stitch).
On the Levi’s 501, selvedge has been a design feature and a study in denim loom evolution through the years. Selvedge relates to the self finished edge of the denim which keeps it from unraveling and grafying. You can identify a pair of selvedge jeans by looking at the inside of the outseam. When you roll the pant leg, you’ll find this crisp strip with a stripe down the middle, and this artful and functional detail (it won’t unravel!) is what sets selvedge denim apart from the rest.
