The SAP Screen Personas Slipstream Engine is a UI5 application that runs in a browser. Unlike Web GUI, the Slipstream Engine was engineered to run on mobile devices, with the expectation that one of the main screen interactions will be touch. So, SAP Screen Personas flavors look like mobile apps when you run them on a tablet or phone.
SAP Fiori can mean different things within a variety of contexts. Fiori can mean a series of specific design guidelines, and it can mean a collection of substantive apps. The most critical point is that SAP Fiori is driving the evolution of user interface, and it is now the forward face of SAP S/4 applications.