Functional requirements, in the context of business analysis and software development, refer to a detailed description of what a system, software application, or product should do.

These requirements outline the specific functions, features, and capabilities that the system or product must possess to meet the business objectives and user needs effectively.

Functional requirements serve as a critical part of the overall requirements gathering and analysis process and are essential for guiding the development or procurement of a solution.

Key aspects of functional requirements:

1. Detailed System Functionality: Functional requirements describe how the system should respond to various inputs or conditions. For example, in an e-commerce system, a requirement might state that "users can add items to their shopping cart";
2. Use Cases and User Stories: Functional requirements are often expressed as narratives, detailing specific interactions between users and the system. Use cases or user stories describe functions or features from the user's perspective;
3. Functional Specifications: These details include technical aspects like data formats, input rules, algorithms, and calculations. They guide developers in implementing functionality;
4. Dependencies and Interactions: Functional requirements identify how different system components or functions interact, ensuring cohesive operation and preventing negative impacts from changes;
5. Acceptance Criteria: These criteria define when a requirement is satisfied, serving as the basis for testing and validation;
6. Prioritization: Business analysts work with stakeholders to prioritize requirements based on factors like business value and criticality, especially when resources are limited;
7. Traceability: Functional requirements should link back to business goals, user needs, or regulatory requirements, ensuring that each requirement serves a specific purpose;
8. Change Management: Business analysts carefully manage changes to requirements by documenting, evaluating their impact, and obtaining stakeholder approval to prevent scope creep;
9. Validation and Verification: Validation checks if the system meets business objectives, while verification ensures compliance with documented requirements;
10. User Acceptance Testing (UAT): Functional requirements are crucial in UAT, where end-users test the system to confirm it meets their needs and expectations.

Overall, functional requirements provide a clear and structured way to document what a system or product should do.