Playbooks in Microsoft Sentinel are based on workflows built in Azure Logic Apps, a cloud service that helps you schedule, automate, and orchestrate tasks and workflows across systems throughout the enterprise.
A playbook is a collection of these remediation actions that can be run from Microsoft Sentinel as a routine. A playbook can help automate and orchestrate your threat response; it can be run manually or set to run automatically in response to specific alerts or incidents, when triggered by an analytics rule or an automation rule, respectively.
Reference:
https://docs.microsoft.com/en-us/azure/sentinel/automate-responses-with-playbooks
https://docs.microsoft.com/en-us/azure/azure-monitor/visualize/workbooks-overview