How are 'non-functional requirements' described?

Non-functional requirements are essential in defining the quality attributes of a system, such as performance, security, usability, reliability, and scalability. In particular, they provide a framework for how a system should behave rather than what it should do, which is typically covered by functional requirements.

By focusing on performance attributes, non-functional requirements ensure that the system meets specific criteria that enhance user experience and operational efficiency. For example, they may specify response times for applications, the load the system can handle, or the level of security required to protect data. These requirements are crucial for the overall quality and user satisfaction with the final product, as they often dictate the system's effectiveness and usability in real-world scenarios.

In contrast, user satisfaction, project financials, and system design specifications do not encapsulate the core essence of non-functional requirements. User satisfaction certainly depends on non-functional aspects but is not a defining property of these requirements. Financial considerations pertain to the economic aspects of a project, while design specifications focus on the implementation details, rather than the quality attributes provided by non-functional requirements.