Glossary Term Definition
The blank space between two facing pages of a book or between adjacent columns of type.
Definition
The blank space between two facing pages of a book, or between adjacent columns of type. In book design, the gutter is the inner margin where the pages meet at the binding. Adequate gutter width ensures that text near the spine remains readable.
Source
No access — Robert Bringhurst — p. 325:
The blank space between two facing pages of a book or between adjacent columns of type.