Bookbinding - a material used to hold the individual signatures of the book block together and to hold the book block to the boards. Compare with cord and kettlestitch (where the kettlestitch is used as the entire support of the book block).
Webster gives a good start at tape, as it is used in bookbinding. Cotton and linen tapes are relatively popular among most bookbinders, as they are easy to work with and reasonably priced. Vellum is a sturdier, more flexible, more archival medium, but it is also more expensive and somewhat prone to tearing if the edges are not cut perfectly straight. Paper can also be used, though it tends to not be strong enough for most books of more than three or four signatures.
Tapes are strips of the materials noted above, generally between 1/4 and 1/2 in. wide, that each signature of a book is sewn on to. Tapes run perpendicular to the spine (so that they can pass every signature), and generally extend an inch or two on each side of the book block, so that they can be attached to the boards. Once the tapes are attached to the boards, the endpapers are pasted over them, to hold the tapes down and provide additonal rigidity.
At least three tapes are used (as three points determine a plane), to give the spine rigidity, and more are used on taller books.
Tapes are used virtually exclusively for binding by hand, as they are not suited to mechancial, commerical bookbinding - cords are far better suited to that purpose.
For an illustration of how tapes are used in bookbinding, see sewing on tapes.
For alternate methods of sewing the book block together, see cord and kettlestitch.