Back vents are zippered openings on the upper back of a snow jacket, often hidden behind a flap. They work by letting the heat that naturally rises from your body escape, creating a chimney effect that pulls cooler air in and pushes warm air out.
These vents are especially popular for backcountry touring and hiking, where you're working up a serious sweat on the uphill. However, there's a catch: if you wear a backpack, the straps and pack body can block the vents, making them much less effective.
Because of this, back vents are less common on standard resort jackets. If you mostly ride lifts and want ventilation, pit zips (underarm vents) are usually the more practical choice. But if you're a touring rider who sometimes goes without a heavy pack—or wants every venting option available—back vents can be a nice bonus feature.