A bookbinding awl is a tool used for punching holes in signatures, in bookbinding. It is distinctly different from a leatherworking awl.
A leatherworking awl widens continually after the the point, whereas a bookbinding awl is of a fixed thickness, generally about 1mm - it will not widen holes in paper. The leatherworking awl tends to have some sort of sharp edge, wheras the bookbinding awl is smooth, completely cylindrical, save for the point. Both awls will have some sort of handle - lightweight plastic on the cheaper ones, wood generally on the more expensive, sturdier ones.
A bookbinding awl is used to punch holes in signatures, or to make the existing holes in signatures easier to put a needle through. It is used to create holes on new signatures that have never been bound into a book, or on signatures from a book that has been torn down, to remove the glue or wheat paste from them, that the needle may pass more easily.
The purpose of a bookbinding awl is to make sewing a book onto tapes, cords, or using a kettlestitch easier. It is possible to just make the holes using a needle - see Plastic box straps, a Leatherman, and handmade paper - a bookbinding adventure - but it is not easy. If you can get a bookbinding awl, even a cheap (US$6ish) one, it is considerably easier than trying to punch the holes using a needle.