An aventail is a neck defence attached to the back of a helmet. It did not protect the throat. Its forward counterpart was the ventail.
A gorget protects the neck and upper chest and is usually of plate. I in fact know of no non-metal gorgets. Some say gorgets sat under breastplates to take spread the weight of the shoulder pieces of a back and breast and they continued to be worn even after other pieces of armour were abandoned eg mid 17th century. Even much later many armies still had them in symbolic forms.
To confuse the issue, a mail gorget was common in the 15th century and is called a standard or standart.
I should be adding this to the main section really. --User 144 23:50, 6 Mar 2006 (CST)