API stands for "Application Programming Interface." It is a set of rules and protocols that allow different software applications to communicate with each other. APIs define how software components should interact.

The "undo" heuristic in UI design is about providing users with the ability to reverse their actions. This feature adds a sense of control and safety for users, allowing them to correct mistakes or change their course of action.

System testing is positioned at the level where the entire software system is tested to ensure its correctness and functionality. It typically follows unit testing and integration testing, coming before acceptance testing in the testing life cycle.

Regression testing can be integrated into the development pipeline by automating regression tests and including them in the Continuous Integration/Continuous Deployment (CI/CD) process. This ensures that every update is tested for ongoing stability and functionality. Manual testing for every update (option 3) would be impractical, and skipping regression testing (option 4) would risk introducing new defects.

The cognitive model in UI design centers on predicting how users will interact with the interface by considering their past interactions and experiences. It delves into user psychology and cognitive processes to create interfaces that align with users' mental models and expectations.

Boundary Value Analysis, a Black Box Testing technique, is significant as it focuses on testing the boundary or extreme values of input conditions, which often reveal errors that might not be apparent when testing typical values.

Incorporating SQA practices into the software development process ensures that quality standards are met, which, in turn, leads to a more reliable product. A reliable product tends to result in higher customer satisfaction because it is less likely to have defects or issues.

Build Management in SCM contributes by automating the process of building software components. It ensures that the right code and dependencies are compiled, integrated, and packaged correctly, enhancing the consistency and reliability of the build process.

The primary purpose of the Observer design pattern is to maintain a one-to-many dependency between objects. This means when one object (the subject) changes its state, all its dependents (observers) are notified and updated automatically. It's commonly used in scenarios where you need to implement distributed event-handling systems or maintain consistent data across multiple objects.

In the Agile model, Quality Assurance is often integrated into the development phase to ensure that the product evolves as per the customers requirements and standards. Agile encourages constant feedback and iterative development, so quality assurance is an ongoing process throughout the development cycle.