UI5 (User Interface 5) is a web-based user interface framework that is used for developing responsive and dynamic user interfaces for web applications. It is a JavaScript framework that is used to build web applications that run on the SAP Cloud Platform, as well as on-premise SAP systems.

Fiori is a design language and user experience (UX) framework that is based on UI5. It is used to create user-friendly interfaces for SAP business applications, providing a consistent and intuitive user experience across all devices and platforms. Fiori applications are designed to be responsive, meaning that they can adapt to different screen sizes and orientations, making them ideal for use on mobile devices as well as desktop computers.

UI5 and Fiori are often used together to create modern, responsive and user-friendly applications for SAP systems. Developers can use UI5 to create custom UI components, while using the Fiori design language to ensure that the user interface is consistent with SAP's design guidelines. This helps to provide a seamless user experience across all applications, making it easier for users to interact with SAP systems and complete their tasks efficiently.