noun
bound-in supplement
Refers to a booklet, poster, or other insert that is physically bound into a book or magazine, not simply inserted loosely.
この雑誌には綴じ込み付録として小冊子が付いています。
This magazine comes with a bound-in supplement in the form of a small booklet.
付録 is a general supplement or appendix, which may be bound in or loose. 綴じ込み付録 specifically means it is bound into the publication.
Compound of 綴じ込み (とじこみ, 'binding in') and 付録 (ふろく, 'supplement').