UAT (User Acceptance Testing) and regression testing serve distinct purposes in the software testing process. UAT primarily aims to validate whether the software meets the user requirements and expectations and ensure its usability and suitability for end-users. On the other hand, regression testing focuses on verifying that changes or modifications that are made to the software have not introduced any new defects or caused unintended side effects to existing functionalities. Regression testing ensures the overall stability and reliability of the software by retesting previously working functionalities in order to prevent regression bugs from surfacing.