The wyvern is a category of heraldry rather than a creature with a mythology of its own. English and continental armory came to distinguish a dragon, which in strict blazon has four legs, from a wyvern, which has two legs, a pair of wings and a knotted, barbed tail, a distinction developed by heralds from the later Middle Ages, not a difference recognised in older dragon-lore, where the two were not separated.
The word derives, through Old French wivre, from Latin vipera, "viper," pointing to its serpentine root. As a charge the wyvern signifies strength and endurance and, sometimes, war or pestilence, and it appears in the arms of English and Welsh families and towns; the red dragon of Wales (Y Ddraig Goch) is technically a wyvern in form. Because it is defined by blazon, the wyvern has no birth-story, no habitat and no legend attached to it as such, it is a way of drawing a two-legged winged dragon, given a name and a set of rules, and its recent prominence in fantasy gaming has treated that heraldic distinction as though it were a species.