Lucid Dream

"''"Often when one is asleep, there is something in consciousness which declares that what then presents itself is but a dream.""

- Attributed to Aristotle, in Hypnogogia: The Unique State of Consciousness Between Wakefullness and Sleep by Andreas Mavromatis

A lucid dream is, simply put, a dream where the sleeping person is aware that he/she is dreaming. By consequence, he/she can exert this awareness over the dream and manipulate it at will. It's not always easy -- sometimes manipulating a dream from the inside can take considerable mental effort -- but when managed it can be fulfilling and and entertaining.

This is Truth in Television, although not terribly common. Most people seem to experience a Lucid Dream once or twice in their lives, but those for whom such dreams are frequent, let alone predominant, are rare.

Anime and Manga

 * In the ending of Kirby Right Back At Ya had Kirby falling asleep and Unlike before when he was awake.

Fan Works

 * In the incomplete Harry Potter and the Wand of Uru by JoeHundredaire/alienyouthct, Harry was plagued by a series of dreams which he thinks may be showing him various alternate futures, and explicitly wishes that they were lucid so that he could ask questions and discover more details.
 * In Astral Journey: It's Complicated, narrator (Emma) learns about this during her coma and partial return to her body.

Film

 * Waking Life: through a series of loosely related dream sequences, Waking Life explores the concept of lucid dreaming and associated psychological concepts. The Dreamer encounters several interesting people who impart information of varying degrees of profundity.