Wikipedia wrote...
DÅjinshi is produced by small amateur publishers outside of the mainstream commercial market in a similar fashion to small-press independently published comic books in the United States. Comiket, the largest comic book convention in the world with over 400,000 gathering in 3 days, is devoted to dÅjinshi.
Unofficial fan-made comics are also called dÅjinshi. Some dÅjinshi continue with a series' story or write an entirely new one using its characters, much like fan fiction.
Manga is lots of people under one name. E.g. Shonen Jump