Performance Testing encompasses a range of tests (including Load, Stress, Scalability, and Volume Testing) to ensure that the software behaves well under expected loads, extreme conditions, and varying workloads. The objective is to deliver a seamless user experience, irrespective of the conditions or demands placed on the software.

"Defect Removal Efficiency" (DRE) metric measures the effectiveness of the testing process. It's calculated as the ratio of defects found before release (by the testing team) to the total defects (found both before and after release). A higher DRE indicates a more effective testing process.

The "Post-release Defect Density" metric gives insights into the number of defects found in the software after its release. A high density suggests that the testing process might have missed issues, while a low density implies effective testing during the development phase.

A "walkthrough" in the review process aims at achieving a mutual understanding of the product. It's a type of informal review where the author leads team members through the product, explaining his or her approach, and it primarily serves to share understanding and gather feedback.

Incremental integration testing involves combining modules one by one and testing them. It is performed in a step-by-step manner, starting with two modules and then gradually increasing the number. This ensures that interface-related errors are detected and fixed.

Stress Testing is designed to push a system beyond its normal limits to see how it responds. It helps in identifying the upper boundaries of a software system and checks its robustness. This is crucial in ensuring that the system will not crash or have unacceptable slowdowns when faced with extreme conditions.

In the Test Planning phase of the Software Testing Life Cycle (STLC), all the planning for the testing activities is done. This includes selecting and setting up the necessary testing tools.

Beta Testing is one of the final stages in the software testing process where the software is released to a limited number of end-users under real-world conditions. The primary purpose is to get feedback from users, ensuring that there are no major failures when it's released to the public and to understand any enhancements users might like to see.

Parallel execution refers to running multiple test cases or test suites concurrently, usually distributed across various machines or cores. This drastically reduces the total testing time, especially in large-scale projects, as it eliminates the need to wait for each test to finish.

A negative ROI in automated testing is typically experienced when there's a high frequency of application changes. This is because every change might require a significant amount of test maintenance, resulting in more time, effort, and cost than manual testing. The essence of automation is to save time in the long run, but frequent changes can counteract these savings.