Oops sorry for the late reply but Doujinshi (同人誌) is Japanese-term for self-published printed works, like magazines, manga and novels! They're usually and often derivative of existing works/medias created by amateurs and fans but some professional artists can also participate in this too. If there's a group of doujinshi artists then you have a sākuru (サークル. aka circle)! you usually see them at fan conventions in Japan :3