An éclair ( or , ; ) is a pastry made with choux dough filled with a cream and topped with a flavored icing. The dough, which is the same as that used for profiteroles, is typically piped into an oblong shape with a pastry bag and baked until it is crisp and hollow inside. Once cool, the pastry is filled with custard (), whipped cream or chiboust cream, then iced with fondant icing. Other fillings include pistachio- and rum-flavored custard, fruit-flavored fillings or chestnut purée. When the icing is caramel, the dessert may be called a (). A similar pastry in a round rather than oblong shape is called a religieuse.
The word comes from the French , meaning 'flash of lightning', so named because it is eaten quickly (in a flash); however some believe that the name is due to the glistening of the frosting resembling lightning.
The éclair originated during the 19th century in Lyon, France where it was called ('Duchess-style bread') or ('little duchess') until 1850. The word is first attested both in English and in French in the 1860s.
Dunkin' Donuts markets Long John donuts as eclairs in the United States. National Eclair Day is celebrated on June 22 in the U.S.
In Brazil, a dessert resembling a miniature is known as a .