Ionic is a hybrid mobile framework for building mobile apps using web technologies instead of native languages such as Java for Android and Swift for iOS.If you can build a static web app using JavaScript,HTML and CSS then you can build mobile apps too thanks to hybrid mobile frameworks such as Ionic .
Ionic uses Apache Cordova for accessing native device features ,uses SASS for styling and Angular.js.The most recent version of Ionic is Ionic 2 which's a completly rewritten framework that uses TypeScript instead of just plain JavaScript and uses Angular 2 instead of Angular.js.