An outrunner in World of Warcraft seems the be a mix between a messenger and a scout. Many things in WoW have this name.
The Alliance Outrunners are four (sometimes just three) level 21-25 elite NPCs in the Barrens, usually near the Southern Gold Road. They have a tendency to gank unsuspecting Horde players, and these victims usually return to gank them at a higher level in return.
Group of blood elves that take care of shuttling goods between Sunstrider Isle and the mainland (which is Silvermoon City). Their travels are not devoid of danger as the Ruins of Silvermoon, which they have to go through, is controlled by the wretched and defective arcane guardians.
The Outrunners' duty is to ensure the safety of those who travel across the plains of Mulgore. Morin Cloudstalker is among their numbers.
Different centaur clans have outrunners.
The Dark Horde have outrunners in the Redridge Mountains.
Some gnoll packs have outrunners.
The Highvale Outrunners are high elves from Quel'Danil Lodge in the Hinterlands.
Night elves have outrunners to watch out for invading forces in Ashenvale.
Some Hozen tribes have outrunners.
Some Yaungol tribes have outrunners.
Outrunner's Bow; which is a bow which can be bought by pvp'ers contesting in the Warsong Gulch.
Outrunner's collection; which is a whole collection of items with the name outrunner as prefix.