A runbook is a detailed guide that provides step-by-step instructions on how to respond to specific types of incidents. It is used by the SOC team to ensure a consistent, organized, and efficient response to incidents. In this case, after the incident investigation, creating a runbook would help standardize the response process for future security incidents, enabling the team to act quickly and effectively. CASP+ emphasizes the importance of having detailed runbooks for incident response as part of an organization's overall incident response strategy.