To bind by stapling sheets together where they fold at the spine.
Securing loose printed, folded, and nested pages with stitches or staples down the middle of the fold (the spine) is known as saddle-stitched binding. The sheaf of papers or signature may be stitched with thread or staples. The name comes from the device or “saddle” on which the folded signatures is placed for stitching — with the saddle in the fold.
Saddle-stitching or saddle-stapling or “bookletmaking” is common for small booklets, calendars, pocket-size address books, and some magazines. Binding with saddle-stitching creates booklets that can be opened up flat.