A bookbinding needle is used for sewing a bookbinding. It is distinctly different from a regular sewing needle.
The eye on a regular sewing needle is signicantly wider than the rest of the needle. The eye on a bookbinding needle is the same width as the body of the needle. This is so that the needle will pass through the holes in the signatures more easily, without widening the hole.
The bookbinding needle as a whole is larger than a normal sewing needle - about .75mm in diameter by 5cm long. This larger size means that the eye, though only the width of the needle, is able to acomodate the thicker thread often used in bookbinding.
Bookbinding needles are as sharp as regular needles, which can be annoying at times - one is only pushing the needle through existing holes, not creating new ones. The sharp point can get caught on the paper and create new holes in the signatures. I often dull my needles a bit with a fine grade sandpaper to avoid this problem.