Gae bolga means 'notched spear', 'belly spear', 'bellows-dart' or possibly 'lightning spear'. It was the spear of Cúchulainn in the Táin. It was given to him by his teacher, the Scottish warrior princess Scáthach, and a special technique was taught to him only.
It was made from the bone of a sea monster, the Coinchenn, that had died while fighting another sea monster, the Curruid. When it impacted its target, hundreds of barbs were unleashed.