(This is true for NorseQuest's setting)
Warbands are a collection of people who have joined together for the express purpose of raiding. Unlike everybody else, they spend all their time training and waiting for raiding season to come rather than working the farms. They also will serve as mercenary forces for hire, not typically caring who their employers are.
Warbands operate like one big felag, with several smaller felags sprouting out from that. The Steelfather leads the entire overarching felag, with each of the Elder Brothers (high-ranking Ironbrothers) having their own felag of Younger Brothers (low-ranking Ironbrothers). Some Younger Brothers lead felags of Stonesons both Younger and Elder.
Some Elder Brothers will renounce any authority they had and don a mask of iron. These men are called 'Ironmasks' and serve as the honor guard for the Steelfather/any other person of interest. They no longer earn orthstirr for their acts, as their face is that of their Steelfather's. They are often times the most powerful members of a Warband — save for the Steelfather, of course.
Warbands reside in halls, typically on the coastline. It is not uncommon to see a hall spring up when a village gets big, as a sort of outpost for a Warband to scout out potential new members/counter rival Warbands in the area. There are a few dozen Warbands out there, with new ones springing up and dying out all the time. New Warbands don't tend to last very long if there isn't a Steelfather at the helm.
Warbands often employ a variety of non-combatants in their ranks (as much as a Norseman can be a non-combatant, anyways). Shapecrafters, ship-builders, seid-workers, Seeressess, rune-carvers, master smiths, and many more are all employed by a Warband.
The most prestigious Warband are the Jomsvikingar, though only because they refuse to acknowledge the Varangian Guard as a Warband and get extremely mad if you mention them in their presence.
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I've settled on Stoneson as the new name for Slagson, by the way.