According to the PMBOK® Guide, specifically within the Collect Requirements process, the Requirements Documentation describes how individual requirements meet the business need for the project.

Components of Requirements Documentation: Requirements can start at a high level and become progressively more detailed as more information is known. A well-structured requirements document typically includes:

Business requirements: Higher-level organizational needs.

Stakeholder requirements: Needs of a stakeholder or stakeholder group.

Solution requirements (Functional and Non-functional): Functional requirements describe the behaviors of the product, while non-functional requirements describe the environmental conditions or qualities required for the product to be effective (e.g., levels of service, performance, safety, security).

Project requirements: These include acceptance criteria and transition requirements.

Impacts to other organizational areas: This identifies how the project ' s result will affect other entities within the organization, such as the help desk, sales department, or existing infrastructure.

Comparison with other options:

A. Business case: This document focuses on the economic feasibility of the project and the cost-benefit analysis. While it justifies the project, it does not typically contain detailed acceptance criteria or specific levels of service.

B. Work breakdown structure (WBS): This is a deliverable-oriented hierarchical decomposition of the work to be executed. It shows " what " is being built but does not describe the qualitative requirements or impacts like levels of service.

D. Risk register: This document records identified risks, their analysis, and response plans. While an impact to another area could be a risk, the formal definition of these elements (especially service levels and acceptance criteria) resides in the requirements documentation.