What is the definition of a myth and a legend?

A myth is a long narrative tale about heroes and their daring quests. A legend on the other hand, is a tale of how something came to be.

Source: My English teacher.

Myth is much longer than legends and subsequently have more characters. Often, these myths are intertwined and form a "mythology". Like the Greek Mythology or Egyptian Mythology. Most often than not, they involve Gods and interactions with man but focus on a "Hero".

Legends are shorter. They can be about the creation of anything: from mountains, seas, to fruits. Or maybe even the legend of a "tradition" or a place.

Remember, myths are about people or deities. Legends are about things.