What is Glamour?

Virginia Postrel asked this question a long time ago, though I didn't answer her at the time.

Her statement the other day that she's adding a section on Glamour to her website reminded me to finally take a crack at answering her old question.

As a first step in defining glamour, I would point to one woman who clearly exemplifies it: Audrey Hepburn. I haven't seen her in many films, but was struck by her amazing, classically glamourous beauty in Roman Holiday, which my wife and I rented a few months ago.

Her character in the movie is a princess who tries to escape public scrutiny for a day to enjoy Rome as a normal person. The interesting thing is that, even when her character's hair is mussed and she is wearing ordinary clothes, there is an aura of glamour about her. Something of a casual confidence and poise that is hinted at. She appears just as comfortable later in the movie, when dressed in full royal regalia.

So for me glamour connotes more than just flashy or expensive beauty. It encompasses an underlying confidence or ease of manner that shows in all kinds of situations (common and formal both).

How's that?