A class of Long-swords that were a little longer, these were the first swords that required both hands to fight with. The term appeared in English around 1300 C.E. and meant what we call now Long-swords, but the term has fallen into common usage to name a type of sword that cannot be used in one hand (at least not without the Exotic Weapons Feat-D&D 3rd ed., natch).
They ranged from 44 to 53 inches, but this was only added to blade length as the handles were around 7 to 9 inches long, just like their earlier counterparts. This added to the weight, making it 3 to 4 pounds, a full pound heavier on average. This different feel to the weapon developed a new type of fighting, wherein closer, tighter movements, in which the body moved around the sword as much as it around the wielder, were used. The Great-sword could hold its own against larger weapons, such as pole-arms and larger axes.The poster child of this variety is the much acclaimed Scottish Claymore, ca. 1300 C.E..
Resources:
Medieval Swordsmanship, by John Clements