In typography, the term gutter refers to the space between columns of type, usually determined by the number and width of columns and the overall width of the area to be filled. Sometimes a rule is used instead of blank space. When laying out pages, gutters should not be so narrow that columns run together. In these cases, the rule line is often used. With standard text type sizes, one pica is the standard gutter space (also called column space). For large type sizes, more gutter space should be used. For type set ragged right, a slightly smaller gutter space works better. Since almost all lines in ragged type are not in full line measure, a small amount of gutter space is "built in." The gutter is also referred to as the column gutter.
In a two-page spread, the gutter is the space between the two pages where the pages are attached to the spine or other binding. This gutter is also known as a gutter margin, back margin, or blind margin.