Exploratory Testing involves testers exploring the software without pre-defined test cases or a specific plan. It's a dynamic process where testers learn the application and simultaneously design and execute tests to find defects.

Regression Testing is the process of testing changes to applications to make sure that the older programming still works with the new changes. It's crucial when there are frequent code changes to ensure that new code doesn't negatively impact existing functionality.

Equivalence Partitioning is a test design technique where input data is divided into different equivalence classes based on their behavior. Testing only one value from each class is deemed sufficient. For a vast range of input numbers, it reduces the number of tests while ensuring effective coverage.

Component Testing: Also known as module or unit testing, this focuses on testing specific functions or modules of an application independently to ensure their performance. It aims to identify any issues at the component level before integrating them into the larger system.

The "Retesting" phase in the bug life cycle is when a specific defect or bug has been fixed and is tested to ensure its rectification. It's a verification process to confirm that the particular defect has been successfully addressed.

Incremental Integration testing involves testing parts of a system sequentially as they're developed. In environments where multiple teams work on different components, this approach ensures that each new piece integrates smoothly with the existing parts, helping detect issues early and reducing integration risks.

A Walkthrough is a type of review where the author leads members of the review through the document based on their understanding. It's informal in nature and often relies on scenarios to provide the reviewers with a deeper understanding. The main goal is to gather feedback and achieve a common understanding.

"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.