Bolas are a throwing weapon consisting of a string (or multiple strings) tied to several weights, with the most common number being three. It can be thrown with the string, but some are attached to handles. The weapon is usually used as a throwing weapon, with the weights hitting the opponent multiple times. However, it can also be used as a melee weapon, much like a mace and chain.
Bolas were used only a few times in Redwall, with Slagar the Cruel being the most notable user. His three-weighted bolas had thongs instead of string, and the ends were tipped with metal, making them a formidable weapon. It was used less notably by Shang Damsontongue and the rest of the Gorge foxes, who chose stone-weighted bolas as their weapons only because they had no metal.
For information on real-world bolas, follow the link.