It can refer to a part of the book, usually, book edges that have been bound or bonded
It can also mean the sheets that have been attached to a single item. This is usually achieved through the use of adhesives, prongs, snaps and so much more. It can also be said to be the entire procedure involved such as piercing, the collection, and folding of the material into the final product.
This refers to the edges of a book where the binding takes place