A Software Tester or QA (Quality Assurance) Engineer is responsible for ensuring the quality and reliability of software applications through systematic testing processes. They collaborate with software developers, product managers, and other stakeholders to understand requirements, identify test scenarios, and create test plans. Software testers design and execute various types of tests, including functional, regression, performance, and user acceptance testing, to detect defects and verify that software meets specified requirements. They document test results, report bugs, and work closely with development teams to resolve issues and improve software quality.