First, "Romance" has nothing to do with romance (such as Harlequins and other mush). A romance is a romance because it's written in romance. That is, in the later centuries of the Roman Empire, there was Classical Latin for the Senate and vulgar Latin in the streets and among the legions stationed for long while among the peoples (exemplified by the two terms "cavallus" vs. "equus"). Other people describing the language of the soldiers called it "romanice." So the term first was an adjective referring to the vernacular language, and then it became applied to the types of tales told in the language.
Medieval romances were categorized into three "matters" by Jehan Bodel, a 13th-century French poet, and his classifications are generally still used:
Matter of Rome the Great -- legends of Troy and Thebes, Alexander, etc.Added to these, however, has to be:
Matter of France -- Roland, Charlemagne.
Matter of Britain -- Arthur and his knights: Lancelot, Parsifal, etc.
Matter of England -- King Horn, Havelok the Dane, Athelstan, Guy of Warwick, Bevis of Hampton, Richard.Romance is an interesting genre because of the culmination of odd narrative effects. Medieval stories of knights and then later novels such as The Bride of Lammermoor, Wuthering Heights, The Great Gatsby, and Lolita usually include the following features:
Auerbach, Erich. "The Knight Sets Forth." Mimesis. Trans. Willard A. Trask. Princeton: Princeton University Press, 1953. 123-142.
Frye, Northrup. "The Mythos of Summer: Romance." The Anatomy of Criticism. 186-206.
---. The Secular Scripture: A Study of the Structure of Romance. Cambridge: Harvard University Press, 1976.
Ker, W.P. "Romance." Collected Essays, Vol. II. Ed. Charles Whibley. London: Macmillan and Co., Ltd., 1925. 310-326.
Sands, Donald B., ed. Middle English Verse Romances. NY: Holt, Rinehart and Winston, Inc., 1966.
Vinaver, Eugene. The Rise of Romance. Oxford: Clarendon Press, 1971.