Ligature is a magical working by tying in a string, thread, or cord one to three knots, usually. Traditionally, for obvious reasons, it is used in binding spells. In ancient Greek times as well as in more recent English times knots were used by sorcerers and sea witches to harness winds and give sailors fair weather for sailing.
In many Wiccan traditions knots are tied in the ritual cord belt of the initiation candidate. The number of knots, one, two or three, in the belt signifies the degree of initiation, first, second or third, which the person is receiving. The knots also magically bind the initiate in place and prevent his/her energies from being dispersed. A.G.H.
Greer, John Michael. The New Encyclopedia of the Occult. St. Paul, MN, Llewellyn Worldwide. p. 274