A tankobon is a collected volume of manga: a book that gathers chapters previously serialized in a magazine, usually five to ten chapters per volume. Most manga is ultimately published and owned in tankobon form.
The tankobon is the unit manga is collected in, and the format shapes the art. Chapters are drawn knowing they will be reread in a bound volume, with volume covers, extras, author comments, and occasionally revised art between the magazine and book editions. A series' volume count is the standard measure of its length, the way cour count measures an anime.
For collectors the tankobon is the artefact itself: uniform spines, cover illustrations that often become the series' most reproduced art, and bonus material that never appears in magazine serialization. Publishers abroad license manga by the volume, so the tankobon is also the international unit of the medium.
The word carries a small historical quirk: it was not coined for manga. Tankobon named any standalone book, and manga borrowed it as collections became standard. Fans use it precisely: a tankobon is the collected volume, distinct from the magazine the chapters first ran in, and from the larger-format kanzenban and other reprint editions. Print runs of landmark early volumes are collectors' items in their own right, and the first-edition obi strip, the paper band around a volume, is catalogued by serious collectors.
In use"The series ran in a weekly magazine, then was collected into tankobon of nine chapters each."