Entitlements and milestones are Service Cloud features that help you track and ensure service level agreements (SLAs) on customer cases. Entitlements define the levels of support that customers are eligible to receive based on their products, service contracts, or warranties. Milestones define the critical steps in your support process, such as first response time or resolution time, and track whether they are completed on time.
You can use entitlement processes to automate actions when milestones are approaching, violated, or completed, such as sending email notifications, assigning cases to queues or users, or changing field values.
Verified References: Service Cloud Consultant Certification Guide & Tips, Set Up and Manage Entitlements and Milestones