dōjinshi; fanzine; self-published magazine
A magazine or book created by a group of like-minded people, often for a niche audience. In English contexts, 'dōjinshi' is widely understood among fans of Japanese pop culture.
I bought a new dōjinshi at Comiket.
He publishes a dōjinshi of science fiction stories.
同人誌 is the self-published magazine or book itself, while 同人 refers to the group or people who create such works.
From 同人 (dōjin, 'like-minded people') + 誌 (shi, 'magazine').