Simple Definition:

A parable is a short story that teaches a moral or spiritual lesson [a lesson about how to behave or what to believe in] by using everyday situations or characters. Parables are often found in religious texts, such as the Bible or the Quran. For example, in the parable of the Good Samaritan, a man helps a stranger who has been attacked, teaching the lesson of showing kindness and compassion to others.

Very Simple Definition:

A parable is a short story that teaches a lesson using everyday situations or characters. For example, in a parable, a story might be told about a kind person who helps someone in need, teaching us to be helpful and caring towards others.