Saddle Stitch Printing are pieces of paper folded and stapled to create pages. Each sheet used yields 4 page faces, so all saddle stitch booklets are in increments of 4 pages.
Perfect Bound Booklets and clamped and glued into a spine. This method is commonly used for large magazines, catalogs, and small books.
Spiral Bound Booklets use plastic spirals to keep their pages in place. The spirals come in different colors, and are a cost-effective way to keep large amounts of pages together.