Your dad likely called it a work shirt. The #menswear crowd lovingly refers to it as a shacket. We simply call it a shirt jacket (and so should you). A heavy-duty, hard-wearing overshirt, it's a practical piece of clothing that will serve you well for the next six months, at least. And while you could likely find some nice vintage versions out in the wild, today's versions have the advantage of a more modern fit. It's got to be just right, you see—roomy enough to sandwich between your button-down and a coat on cold days, but tailored enough to sport by itself over a plain T-shirt or with a shirt and tie as a rugged blazer replacement. Trust us, you'll get more use from this ideal layering piece than you'd expect.