Which document describes the application architecture and its various components?

The System Design Document is critical in providing a comprehensive description of the application's architecture, detailing the various components, their interactions, and the overall design framework. This document serves as an essential guideline for developers and stakeholders, outlining how the system should operate and how different modules or layers are intended to work together. By defining the architecture clearly, the document ensures that all parties involved have a shared understanding of the system's structure, facilitating better communication and reducing the risk of misunderstandings during the development process.

On the other hand, the Requirements Definition focuses on the needs and expectations of stakeholders, outlining what the system should achieve but not necessarily providing the architectural details. Test Plans are designed to validate that the system meets its requirements through testing scenarios, while the Security Policy Document outlines the security protocols and measures in place to protect information, rather than the application architecture itself.