On its official site, it says:
Android Jetpack is a set of libraries, tools and architectural guidance to help make it quick and easy to build great Android apps. It provides common infrastructure code so you can focus on what makes your app unique
Technically, it is the support library, android-ktx and the Android Architecture Components re-branded as a single modular “entity”.
This is why all non-Android extension libraries like support, etc. are re-packaged to androidx.**.
Quote from Alan Viverette (from Android Framework Team):
Jetpack is a larger-scoped effort to improve developer experience, but AndroidX forms the technical foundation. From a technical perspective, it’s still the same libraries you’d have seen under Support Library and Architecture Components.
As best practices change, you may also see libraries in the androidx.* package that are not included in Jetpack.
See https://developer.android.com/topic/libraries/support-library/refactor for more info.