Horde Expedition is the combined forces of the horde in Northrend, spearheaded by the Warsong Offensive.

Reputation

Half of the reputation gains from the Horde Expedition's four sub-factions count towards this the Horde Expedition's reputation. Therefore, you must have two of the four sub-factions at Exalted in order to be exalted with the Horde Expedition, or the equivalent amount of reputation spread across all four.

Wrath heroics (as well as normal level 80 instances: Utgarde Pinnacle, The Culling of Stratholme, The Oculus, Halls of Lightning) will give spillover reputation with all the Horde Expedition forces concurrently without a tabard equipped.

The rewards are low-level, but Schematic: Mechano-Hog is of interest to engineers.