A big idea that pops up over the course of a literary work (story, play, poem, etc.)—and about which the work may offer a certain message.
Because it is located in the realm of ideas beneath the surface of a text, theme is sometimes difficult to identify. A reader must closely examine the surface—a story’s characters, plot, and literary devices—to find the theme(s) hidden below .
The above examples demonstrate that a theme is best articulated as a single word (often an abstract noun) or a short phrase. However, one can go on to ask what the literary work is saying, specifically, about a particular theme. That is, one can distill a certain thematic message, which may be evident in both the literary work and the reader’s experience.
Moral: A simple, instructive thematic message whose delivery is the primary purpose of a literary work. (See The Lion and the Mouse)
Thematic truth: A more complex, descriptive message whose validity can be debated and whose presence does not dominate the literary work. (See Romeo and Juliet)
Motif: A repeated narrative element (an image, a phrase, a stylistic or structural device, etc.) that may have symbolic significance. In general, a motif is more concrete than a theme. In Romeo and Juliet, night and day imagery is a motif.
Source: Canada, Mark. “Glossary of Literary Terms.” University of North Carolina Pembroke, n.d. Web. 9 Oct. 2012.