copyAlarmString is a free-form text varbind carried in the copy-operation alarm trap, per its description as "an generic string value in the TRAP object". An admin reads this in the trap to get the human-readable detail of what happened during the copy operation, since copyAlarmLevel alone only conveys severity, not the specific cause. For example, copyAlarmString might contain a message like "scp transfer failed: connection timed out" in a trap generated by a failed copy to a remote server.