Comiket is a semi-annual dōjinshi fair, held in Tokyo, Japan. It is a convention for selling dōjinshi and self-published Japanese works. The attendance in winter of 2016 was over 550,000 people.

Comiket is a dōjinshi fair founded in 1975 by Yoshihiro Yonezawa and friends with only around 600 attendees. That number has since grown to 550,000 people. It is held in August and January every year in Tokyo. It is a convention primarily for selling self-published works ranging from musical covers to stories to art.

Sellers are referred to as 'circles', and are listed in the convention catalogue in circle cuts.

A graph comparing Dōjin circle count over 17 Comikets

Dōjin circles counted by the original work being made derivative works of (parodied), from Comiket 84 (August 2013) to Comiket 91 (December 2016)

Links:

Wikipedia page

More information on circles and circle cuts