n. A sliding knot for climbing or caving use. Named for Dr Karl Prusik who invented it for climbing use.
A loop of 6 or 7mm static rope is wound around a rope of larger diameter and slides freely along it until weighted in either direction when it will jam.
The knot was used extensively for ascending ropes prior to the invention of the jumar, now it is more a device for impromptu rope rescue systems and glacier travel.
Other variants are the Bachman knot and the French Prusick both of which operate in the same manner but provide slightly different locking and unlocking properties. All three knots have good applications but to an extent all three have now been replaced by micro-jumars such as the Petzl Tibloc or the Wild Country Ropeman.
Aspiring climbers and cavers should still learn their construction and use, for emergencies and those applications where a micro jumar is not suitable.