A sleeveless vest, warm and snug, sometimes insulated and fur lined, that's a gilet. Some gilets are lighter and serve as windproof or light jackets, while others do heavier duty as winter garments or even ski clothes.
The outer surface of a gilet may be denim or a water-resistant fabric, or something wind-tight and warming. The only common feature of all gilets is the vest-like structure, so that it leaves free arm movement. Meet the outdoors in a gilet.