In Runescape, a skill released in early 2008. Once a decent level is obtained in the skill it can be incredibly useful, but do to the requirement of shards and charms to train it, this can be rather difficult for some players.
When training Summoning, you must use a blank pouch, colored charm variant on the familiar you make, a certain amount Spirit shards, and a secondary item unique to the familiar.
Likely one of the most popular familiars, the Spirit Terrorbird can be used to hold a nice extra 12 items and can make you run for a very long time provided you use the scrolls for it, or virtually forever depending on your weight and Agility level.
Summoning is a very useful skill in Runescape released January 15, 2008.
Player one: What level is terrorbird?
Player two: Just click on the skill guide you lazy git.