Fan fiction (alternately referred to as fanfiction, fanfic, FF, or fic) is a broadly-defined term for fan labor regarding stories about characters or settings written by fans of the original work, rather than by the original creator. Works of fan fiction are rarely commissioned or authorized by the original work's owner, creator, or publisher; also, they are almost never professionally published. Fan fiction, therefore, is defined by being both related to its subject's canonical fictional universe and simultaneously existing outside the canon of that universe. Most fan fiction writers assume that their work is read primarily by other fans, and therefore tend to presume that their readers have knowledge of the canon universe (created by a professional writer) in which their works are based.

Media scholar Henry Jenkins explains the correlation between transmedia storytelling and fan fiction:

The encyclopedic ambitions of transmedia texts often results in what might be seen as gaps or excesses in the unfolding of the story: that is, they introduce potential plots which can not be fully told or extra details which hint at more than can be revealed. Readers, thus, have a strong incentive to continue to elaborate on these story elements, working them over through their speculations, until they take on a life of their own. Fan fiction can be seen as an unauthorized expansion of these media franchises into new directions which reflect the reader's desire to "fill in the gaps" they have discovered in the commercially produced material.

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