Fan Fic Header

Fan Fic Header or just Header is a text that is included at the beginning of a Fanfic or in any post announcing a Fan Work, to covey some basic information related to the work in question.

While the format may vary depending on the conventions of the place where the fan work is posted, the typical header contains most, if not all, of the following items:

Fandom
Title
Author/Artist/Maker/Vidder
Rating
Character(s) and Pairing(s) (if applicable)
Summary
Disclaimer
Genres
Word Count (for fic) / Length (for videos and podcasts)
Media used (for fanart)
Format (for example: drabble, short story, WIP...)
Type: Standalone, prequel to ___, sequel to ___ , series of stories it belongs to:
Archive (either yes/no, to say whether the author gives permission for the story to be archived, or to indicate what archive it will appear in - this was seen in fan works passed on mailing lists, years before directly posting in fandom archives became the norm)
Content Warnings
Spoilers/Timeline -- when a story is set; what episodes you should have already seen to enjoy the work.
Author's Notes
Thanks to the Betas

Headers are a relatively recent convention within fandom, dating from the Usenet era around mid 1990s. Before that, authors of fan works distributed thorough fanzines and early mailing lists rarely gave information beyond title and fandom, and, occasionally, a vague "age statement" to inform that the following fan works could have "Adult Concepts" (usually meaning Lemon and Slash stories) to cover their asses in the case that some worried parent attempted to sue the fanzine creators for providing their dear children smut. As fandom expanded in the internet and fan works became to increase in number, it became a necessity to identify and provide information about the work in question, making the fanfic header a promotional tool. In the years before blogging, headers also served as a communication tool between the creator and other fans, since authors used the initial notes to convey personal information, inside jokes, thanks to other fans, and even insight about their own work and creative process.

Most fan works archiving sites (like Fanfiction.net and Archive of Our Own) have automatized the standard headers by including most of the information necessary for the fic in the uploading form and them embedding it in the work page. Fandom communities in blogging sites usually have a header template to be used by any of the members when posting fan works. For other sites, there is a Fanfiction Header Builder tool that easily create headers to be posted in standalone webpages, blogs, and other social media.

Some writers who host their own works put much or all of this information into a footer instead of a header.