Mise-en-abime \mise-en-abime\, n.

1. Literally, "placement en abîme," where "en abîme" itself refers to the habit of representing a small shield inside a larger one in traditional heralds and coats-of-arms.
2. Most any "story-within-a-story" situations can be called an example of mise-en-abîme. The device is especially common in modern literature, television and films, but it occasionally appears in art, E.g. a religious scene tucked into the background of a genre scene with very different kinds of activity.