A posture collar is a rigid collar used in BDSM and fetish play that is wide enough to restrict movement of the neck. Posture collars help in maintaining posture, keeping the chin high and the neck extended. Posture collars typically flare widely at the front to reach from the chin to the collarbone, preventing the wearer from hanging their head or looking downward.
On Etsy you will find some wonderful examples of such a collar. I like this one very much:
It looks so elegant and is made by Olga and sold on Etsy.
Did I say I simply love the posture collar, as Carrie is wearing in Training Carrie?