One of nine principle characters from Victor Hugo's "Les Misérables". All young, all adorable, all French, all usually portrayed in fanfic as being ready and willing to engage in debaucherous sexual activities with one another. Mention of a Frenchboy or Frenchboy slash rarely fails to evoke a fangirlish "squee".
Enjolras, Combeferre, Courfeyrac, Jean Prouvaire, Joly, Bossuet, Bahorel, Feuilly, and Grantaire are all Frenchboys.(One might include Marius in this mix, too.)