Ionic is an UI framework initially made to create mobile hybrid applications by providing Angular components rendering with a native look on each platform.
In their latest version built with Web Components rewrite, they officially support web apps in addition to mobile and desktop hybrid apps providing iOS and Android (Material design) looks for the components.
Since Ionic v4 move to embrace Web Components and native build tools for each framework, Ionic CLI now uses Angular CLI under the hood to perform all build-related task, so we can completely skip it and have one less dependency in our package 😉.