Something that occurs frequently in a literary work (or work of art) for a specific purpose.
For example, in a collection of artwork an artist could use the color blue as a motif. It’s something that is found commonly throughout and could be used to show sadness.
In literary works, a motif is usually a common idea that is a theme throughout the work. In Hamlet, ears and hearing are a motif used to show how language can be used for truth or deception. To get a better idea of what a motif is in a literary work, the link below will take you to a page explaining the other motifs in the play Hamlet. http://m.sparknotes.com/shakespeare/hamlet/themes.html