Free Folk

The wildlings or free folk are a race of people who live beyond the Wall, still on the continent of Westeros but beyond the northern border of the Seven Kingdoms. The wildlings consist of many fractious tribesfolk and village-dwellers, some reasonably cultured, others savage and hostile. They spend much of their time fighting one another, aside from the times when they are unified by a King-beyond-the-Wall.

The people of Westeros believe that the Wall exists to protect the realm from the wildlings, but the Night's Watch knows it is really to defend against the near-mythical Others who almost destroyed the world eight millennia ago.

In the books
In the Song of Ice and Fire novels the wildlings consist of various factions, such as the people of Thenn, raiders from the Frozen Shore and townsfolk from Hardhome. At the time of the books they are unified under a King-beyond-the-Wall, Mance Rayder, a member of the Night's Watch who fled the Wall and betrayed the Sworn Brothers. With the Wall grievously under-strength, there are fears that the wildlings may try to invade and that Lord Eddard Stark might have to lead his banners against them in a punitive strike.