What is the Setup Audit Trail and when would an admin use it?

The Setup Audit Trail records changes made to the Salesforce org's configuration (metadata) by administrators. It logs the date, time, the user who made the change, and what was changed (e.g., "Created custom field Opportunity.Discount__c"). Accessible from Setup > Audit Trail. It retains up to 180 days of history (downloadable as CSV for longer history). Use cases:

1. Investigating who made an unintended configuration change.
2. Compliance auditing.
3. Troubleshooting newly introduced bugs by correlating them with recent config changes.
4. Reviewing changes made by external consultants or other admins. It does not track data changes — for that, use Field History Tracking or Field Audit Trail.