Ionic is an HTML5 mobile app framework with a free, open-sourced SDK, used for hybrid mobile app development. Built on top of frameworks AngularJS and Apache Cordova, Ionic provides a large amount of resources for hybrid mobile app development.
Ionic is built with HTML5 because the the developers believed that the markup language would dominate on mobile apps like it has on mobile. With browser technology for desktop computers being advanced enough to be built into mobile technology, people were spending more time on their mobile devices than they would on computers. Ionic took advantage of this by building their framework for mobile development, focusing on native or hybrid apps.
Ionic is the main framework we use for developing mobile applications, provided with the SDKs it gives us and it's built on top of the frameworks AngularJS and Cordova. We use Ionic's UI components to create forms, buttons, lists, navigation, popups and prompts, tabs, sliding boxes, etc. This helps us structure the app's pages while we work on the CSS and back-end servers to make it fully functional.