What is defined generally as an artistic chef d'oeuvre or masterpiece, why and when?

Recently I was listening to a radio interview in France with the actress, Catherine Deneuve, just before the launch of her new film, "Sage Femme/the Midwife".  The interviewer asked her if she though this film was a chef d'oeuvre.  Her reply interested me because it does not just apply to the "Seventh Art" of films.