noun, noun or participle which takes 'suru', transitive verb
special issue; extra number
Refers to an additional issue of a periodical, such as a magazine or journal, published outside the regular schedule. Also used for the act of issuing such an extra number.
この雑誌は年に一度、増刊号を発行している。
This magazine publishes a special issue once a year.
To commemorate the conclusion of the popular manga, the publisher decided to issue an extra number.