A rather nifty container for dispensing milk, produced by Dean's Farms and available largely in the mid-Atlantic United States. It holds a pint (about 500 mL) of either skim milk, 1% reduced-fat milk, 2% low-fat milk, whole milk, chocolate milk, low-fat chocolate milk, or strawberry milk.
The container's shape is likely a design trademark, like the contour bottle used by Coca-Cola; no other milk producer bottles their milk in exactly the same way. It is made of plastic, not paper like most milk cartons. It fits in a vehicle's cup holder. It has a twist-off cap. Of course, it is recyclable.
Dean's also bottles several items that are not milk in the "chug" packaging: for example, you can buy orange juice chugs. During the Christmas season, they also sell eggnog chugs. The chug is also available in a cute six-pack of 8 oz (about 250 mL) bottles, or a "mega chug" of 32 oz in capacity.
I once chugged a mega chug of chocolate milk in a span of roughly 2 minutes. I felt kinda weird after that.