Terminology
The legenda (literally, that which is for reading) included facts which were historically genuine, as well as narrative which Christians now class as unhistorical legend. The term is a creation of the Middle Ages, and has its source in the reading of the prayers used in religious services. Since the days of the martyrs, the Catholic Church recalled to mind her famous dead in the prayers of the Mass and in the Office, by commemorating the names noted in the martyrologies and making mention of incidents in their lives and martyrdom. When the lectio became a matter of precept, the reading matter in the office for the day became in a precise sense legenda (that which must be read).
After the 13th century, the word legenda was regarded as the equivalent of vita (Life) and passio (suffering), and, in the 15th century, the liber lectionarius is comprised under what is known as "legend". Thus, historically considered, legend is the received story of the saints.
Read more about this topic: Legendary Material In Christian Hagiography