The "think-aloud" method is used in Usability Testing. Participants are asked to speak their thoughts aloud while they perform tasks, providing insights into their cognitive processes, decision-making, and how they navigate and interact with the interface, highlighting potential usability issues.

Defect Detection Percentage (DDP) is a vital metric that calculates the ratio of the number of defects detected to the total number tested. It provides insight into the efficiency of the testing process, giving an understanding of how well the testing phase is identifying issues.

Postman is a versatile tool designed for API testing. With microservices, the emphasis is often on ensuring API contracts and interactions are reliable. While tools like JUnit and Selenium are great for unit and UI tests respectively, Postman offers the flexibility required for varied microservices.

Usability Testing ensures that the designed application is user-friendly, intuitive, and easy to use. Especially for elderly users who might not be familiar with modern tech conventions, ensuring the app's usability is crucial to prevent any potential frustration or challenges during their interaction.

The "Pesticide Paradox" principle states that just as pesticides become ineffective when pests develop resistance, similarly, test cases lose their effectiveness if they are not regularly reviewed and updated. New defects can't be found when using the same tests repeatedly.

One of the main challenges with automated testing is ensuring that test scripts can be easily maintained over time. As the application evolves, the test scripts need to be updated, making maintenance a pivotal concern for ensuring the relevance of automated tests.

"Interoperability Testing" ensures that the mobile application can operate and interact as expected with other applications. This ensures that there's no interference or unexpected behavior when two or more apps are used simultaneously.

Platform Compatibility is the criterion that evaluates an automation tool's ability to run tests across different operating systems, browsers, and devices. A tool with high platform compatibility ensures consistent test execution across various environments, making it invaluable for diverse software and application landscapes.

Error Guessing is an experience-based testing technique where testers use their intuition and experience to guess where defects might be located in the software. This technique leverages the tester's past experiences and knowledge of common defect patterns.

The "big bang" approach differs from typical non-incremental methods in that, in the "big bang" approach, the integration testing is deferred until all individual modules are developed. This could lead to challenges in identifying defects because everything is tested at once.