noun
Refers to a special edition of a periodical, magazine, or journal dedicated to a particular topic.
今月の特集号は環境問題を取り上げている。
This month's special issue covers environmental issues.
特集 means 'special feature' or 'special report' and can be used more broadly, while 特集号 specifically refers to a special issue of a publication.
Compound of 特集 (とくしゅう, 'special feature') and 号 (ごう, 'issue/number').