This read-only enum reports whether the stack is currently idle (running(1)) or actively executing the Stack Management Update protocol (updating(2)), the internal handshake that synchronizes stack-wide configuration across switches. The description explicitly tells management stations to check this object when a SET to a stack-wide attribute returns genErr, since a SET made mid-update is rejected until the protocol finishes. An admin seeing updating(2) after adding a switch to the stack knows to wait before retrying a failed configuration change rather than assuming the SET itself was wrong.