tacketed binding
OAB Definition
book blocks or individual signatures held in a cover by lengths of thread, leather, or vellum which are twisted or tied to form a temporary or informal binding. Tackets filled a similar role in the Eurpoean middle ages as staples do today. A common tacket was made of twisted, dampened vellum. Upon drying, the vellum compresses and hardens, creating a sturdy connection.
Tackets that hold individual sections are called primary tackets. Those that held an already bound textblock into a cover are called secondary tackets.