Android is a mobile operating system owned by Google. It runs on a modified version fo the Linux kernel and comes pre-installed with various open-source software.
Android code can be written in any language that can run on the JVM. The most commonly languages (and the ones I use) are Java and Kotlin. More languages that are used for the same purpose include Scala, Groovy and C++.
I use the Android ecosystem to build native apps using Java and Kotlin.