Ad usum Delphini means “for the use of the Dauphin”. It is a collection of classical Greek and Latin texts used by the Duke of Montausier for his education of the Grand Dauphin, son of King Louis XIV. This text was on the cover of the traditional texts which had been purified because they contained passages considered too embarrassing or inappropriate for the youth. The collection includes 64 volumes published from 1670 to 1698. Authors affected were Homer, Aristophanes, Plautus, Terence, Ovid, Juvenal and Martial.
Even Racine's Esther was amended:
Today, this expression is used pejoratively to indicate a work expurgated in order to be put in all hands.
References
Ad usum Delphini Wikipedia(Text) CC BY-SA