I've seen a number of things listed as doujinshi but not linked to any other series. Sometimes in the description, it says "original doujinshi". If doujinshi are fan works, stories based on already existing anime, then what the heck is an original doujinshi?

No, it is not an oxymoron.

Quote from Wikipidea

Dōjinshi (同人誌?, Dōjinshi, often transliterated as Doujinshi) are self-published Japanese works, usually manga or novels. They are often the work of amateurs, though some professional artists participate as a way to publish material outside the regular industry.

Sure, usually, it's just fanfiction material, but it can be original too.

[img]http://i196.photobucket.com/albums/aa229/azrinirza/makotoshinkai1_zpse3901c5a.gif[/img]
Everyday I'm tumblin'

Ah, okay. I didn't realize that they were defined by being self-published. Thanks 🙂

As defined for this site, there is no such thing as "original doujinshi". For the purposes of the database, all oneshots and related things ARE NOT "original doujinshi". The only thing to be defined as doujinshi is anything related to an original series

Which means that parts of the database are wrong because people continue to misunderstand our policies

A just ruler amongst tyrants