extra collar around waist to keep snow out? If we are thinking of the same thing it is usually inside the jacket and slightly higher with a hem cord. A ski jacket comes to mind.
I believe he is talking packs. It is the material at the top of the pack opening with a draw string. It keeps snow from being blown under the lid and into the pack. You can also stuff the pack fuller and use the collar to contain it above the actual pack. I'm no expert