FURPS (Functionality, usability, reliability, performance, supportability) is a model for classifying software quality attributes (functional and non-functionalrequirements):
Model
Functionality - capability (size and generality of feature set), reusability (compatibility, interoperability, portability), security (safety and exploitability)
Usability (UX) - human factors, aesthetics, consistency, documentation, responsiveness
Reliability - availability (failure frequency (robustness/durability/resilience), failure extent and time-length (recoverability/survivability)), predictability (stability), accuracy (frequency/severity of error)
The model, developed at Hewlett-Packard was first publicly elaborated by Grady and Caswell. FURPS+ is now widely used in the software industry. The + was later added to the model after various campaigns at HP to extend the acronym to emphasize various attributes, such as Design Requirements, Implementation Requirements, Interface Requirements and Physical Requirements.