Short for doujinshi , which refers to self-published works. While doujinshi can cover any genre, in the context of yaoi, it almost always refers to fan-made manga, novels, or art books featuring existing characters from popular anime or manga series.
In Japan, while the production of doujinshi technically infringes on copyright, it exists in a "grey area." Original authors and publishers typically tolerate it because it fosters a dedicated fan base and helps keep their franchises popular. Modern fan culture often engages with yaoi dj through: yaoi dj