From the SRD5: Dragons are large reptilian creatures of ancient origin and tremendous power. True dragons, including the good metallic dragons and the evil chromatic dragons, are highly intelligent and have innate magic. Also in this category are creatures distantly related to true dragons, but less powerful, less intelligent, and less magical, such as wyverns and pseudodragons.
From wikipedia: A dragon is a large, serpentine legendary creature that appears in the folklore of many cultures around the world. Beliefs about dragons vary drastically by region, but dragons in western cultures since the High Middle Ages have often been depicted as winged, horned, four-legged, and capable of breathing fire. Dragons in eastern cultures are usually depicted as wingless, four-legged, serpentine creatures with above-average intelligence.
