SAPUI5 and SAP Fiori are two related but distinct components of the SAP user experience. SAPUI5 is a development toolkit used to build web applications with a consistent and responsive user interface. It provides a comprehensive set of UI controls and libraries for creating SAP applications.
On the other hand, SAP Fiori is a design concept and a set of user interface guidelines provided by SAP. It focuses on delivering a simplified and intuitive user experience across various devices and platforms. Fiori applications are built using SAPUI5, but they also incorporate specific design principles and patterns defined by the Fiori design guidelines.
In summary, SAPUI5 is the development toolkit, while Fiori is the design concept that utilizes SAPUI5 to create visually appealing and user-friendly applications.