A revenant is a ghost or animated corpse that has returned from the grave: something that we might now refer to as a zombie. Armand dismisses the Eastern European vampires Claudia and Louis have seen as revenants, implying that they are effectively a different species. In French, "revenant" means "returning."
According to mythology, the Roman Goddess of love, Venus, was born out of the sea as a fully grown woman. Botticelli's famous painting, "The Birth of Venus", captures the moment: