The inner margin or blank space separating two facing pages in a bound book, or the vertical space between columns of text on a single page. In traditional letterpress, it also refers to the physical wood or metal furniture placed in the chase to create this spacing between type pages.
Heard on the job
Increase the gutter by a quarter inch so the text doesn't get lost in the binding fold.
Insider tip
Beginners often forget to account for the binding method, resulting in a gutter that is too tight to read once the book is bound.