Steward is a rank within the Night's Watch. They are tasked with keeping the order supplied and undertaking domestic and support duties.
Stewards generally do not serve a combat role, typically do not partaking in rangings, and are not considered authorities on the structure of the Wall itself. In practice however, stewards can join in major battles if necessary, can accompany rangers in a support role on great rangings, and can also be assigned to sentry duty on top of the Wall.
The Stewards collectively report to the First Steward, who in turn reports to the Lord Commander of the Night's Watch.