The term claymore has come to the modern sword enthusiast to refer to the two-handed swords of the Scottish Highlanders. This arrises from the late 18th century where the "glaymore" is stated as being a such a weapon.
They could be up to a metre and a half long, and tended to come with a heavy pommel, with noticeable fullers running down the centre of the blade. It would be used double-handed, tended to have a crossguard which might curve forward, away from the hands, and sometimes ended in spatulate swellings. Some later examples have quatrefoil designs at the end of the crossguard.
Properly used, these were weapons that carried the weight and momentum to drive through an enemy's attack, even through his weapon's blow, and cause a wound. These were useful for trapping an opponent's blade, and, with a deft twist, disarming him (or pulling him close enough to either head-butt or stab with the dagger you had in your stocking top).
Its name is an Anglized version of the Gaelic claidheamh mor or "Great Sword" refers to a basket hilted broadsword. The term claymore (as "clymore") was not recorded until 1678 and claidheamh mor is a neologism from 1745. Unfortunately these chroniclers were English, but no Scottish historical references have survived. In 1772 a reference to Highlanders refering to two handed swords as claidmeah da laimh (literally:two handed sword).