Legends (derived from Latin legenda) are stories in oral tradition passed on by word of mouth. They narrate human actions, and are usually old but are believed to have taken place within human history. Legends have often been transformed over time to keep them realistic.
The word is also used for famous or historically significant people, places, events, etc. We sometimes say of someone who is extremely famous that they are a "legend" or "of legendary fame".
Examples of legends are Ali Baba, the Fountain of Youth, Paul Bunyan, Bogeyman, Kraken, Sirens, Atlantis, the Loch Ness Monster, Bigfoot, and Yeti. Some legends are stories about real people; others are not. Odysseus and Robin Hood for example may have been real but most the stories about them are definitely fiction.
For some places, legends are the earliest history. For example, the origin of ancient Rome is known only from legends, as are the earliest dynasties in the history of China.