Warband

The Guild Wars 2 Wiki has an article on Warband.

A warband is the name of groups of Charr. Most warbands have between five and twenty members within them and all warbands act under the command of a High Legion. To the Charr, warbands are comparative to a human's family. The Charr are entered into a warband once they leave a Fahrar, and it is important that a warband's new Charr functions well within that warband, otherwise that Charr would be a hindrance to the group. Although a Charr may change their warband, it is rarely done and the first warband will always hold a special meaning to the Charr. If a Charr loses or leaves its warband, it becomes known as a gladium.

The first part of every Charr's surname is named after the warband they are in. When Charr change warbands, their surname also changes.