A Non-Functional Requirement (NFR) refers to criteria that specify how a system should perform rather than what it should do. These requirements focus on aspects such as performance, security, usability, and reliability. For example, an NFR might state that a website should load within two seconds or that it must be accessible to users with disabilities. NFRs are essential for ensuring that a system meets user expectations and operates effectively in real-world conditions. They help guide the design and development process, ensuring that the final product not only functions correctly but also provides a satisfactory experience for its users.