A héroïde is a term in French literature for a letter in verse, written under the name of a hero or famous author, derived from the Heroides by Ovid. It was invented by Charles-Pierre Colardeau.
Source
Artaud de Montor, Encyclopédie des gens du monde, v. 13, Paris, Treuttel et Würtz Treuttel et Würtz, 1840, p. 762-3.