A Tankōbon is the Japanese term for a compilation volume of manga stories for a given author.
Japanese manga is typically published in weekly/monthly compilations (such as Afternoon or Shonen Jump). These compilations often have hundreds of pages and dozens individual story lines by different authors. Since these weekly/monthly editions are printed on very cheap newsprint, they are considered disposable. Tankobon collect multiple chapters from a single author and reprint them in a roughly paperback-sized volume on higher quality paper.