SoapUI is an open-source web service testing application for service-oriented architectures and representational state transfers. Its functionality covers web service inspection, invoking, development, simulation and mocking, functional testing, load and compliance testing. API: A set of rules and protocols for building and interacting with software applications. APIs define how different software components should interact. Endpoints: Specific paths in an API where certain functionality is exposed. Request Methods: Standard HTTP methods like GET, POST, PUT, DELETE used to interact with APIs.