What is Maven repository in Android Studio?

Im not Java guy but from fast lookup in google:

Maven is build and dependency management tool (helps in building project and downloading dependencies).

Jcenter looks like repository of available libraries (is source for all dependencies downloaded by maven processes).

A maven repository is a "repo", public or private, to store libraries, plugins and in general artifacts.
It is not related to Android Studio or another IDE.

JCenter is one of the maven repo.

JCenter is the place to find and share popular Apache Maven packages for use by Maven, Gradle, Ivy, SBT, etc.

Other common repo used in Android are:

• Maven Central
• Google maven repo

In a gradle script you can find them in the repositories block:

/**
     * The repositories block configures the repositories Gradle uses to
     * search or download the dependencies. Gradle pre-configures support for remote
     * repositories such as JCenter, Maven Central, and Ivy. You can also use local
     * repositories or define your own remote repositories. The code below defines
     * JCenter as the repository Gradle should use to look for its dependencies.
     *
     * New projects created using Android Studio 3.0 and higher also include
     * Google's Maven repository.
     */
repositories {
        google()
        jcenter()
    }