A "legend" can refer to a story, a body of stories, a well-known person or a key that explains symbols. The word originates from the Middle English word "legende," which describes written accounts of the lives of saints, and from the Medieval Latin word "legenda," which means to be read.
In reference to stories, "legend" usually refers to fantastical stories with supernatural or mythical beings, and this carries over to bodies of stories centering around the same figures, such as the legends of King Arthur. King Arthur himself also qualifies as a legend when used in reference to a well-known person or character. A legend can also be a key that explains symbols used to illustrate meanings on maps or other documents.