What is UI5?
The UI5 framework provides concepts such as components (referred to in other frameworks as applications and/or reuse composite components), Model-View-Controller pattern to structure the application, routing to manage navigation between views, integrated data binding and more.
In UI5, so-called controls (respectively UI elements; in Simplifier they are called Widgets) are used to assemble the user interface. A major benefit of UI5 is that they come with a wide variety of bread & butter, layout, and complex controls to build your application.
Learn more about the difference between OpenUI5 and SAPUI5 here.
What is SAP Fiori?
Is UI5 self-contained or does it use open source?
UI5 uses open-source software. There are a number of open-source libraries that are included in the UI5 framework. The best-known example of using open-source is jQuery.
What is a UI5 control?
UI5 controls are the built-in offering of the UI5 framework for writing UI elements. A special feature is the out-of-the-box data binding support, which allows the controls to be easily bound to data from different models.
Take a look at this blog post to learn more about UI5 Framework and UI5 Web Components.