What is Folded Corner Trim Defect

A Folded Corner Trim Defect, also known as a dog-ear trim-in, happens when the corner of a page is accidentally folded before the book block is trimmed. Since the folded area is hidden from the cutting blade, it does not get cut together with the rest of the page. When the page is opened later, the untrimmed part appears as an extra triangular paper flap or uneven corner inside the finished book.

This is a production defect, not a design feature. It can happen during folding, gathering, pressing, handling, or final trimming if a folded page corner is not noticed before the book block goes through the cutter.

In Japanese printing and bookbinding, this defect is sometimes called fukumimi（福耳）, which literally means “lucky ear.” In everyday Japanese, fukumimi can also refer to a large, full earlobe, which is traditionally associated with good fortune or wealth. In printing, the term is used because the untrimmed folded paper flap looks like an ear. Although the word has a lucky meaning, in book production it still refers to a trimming defect that should be caught during quality control.