Android is an open-source and Linux-based operating system. It was first introduced on Nov 5, 2007. It was originally developed by Android Inc. and subsequently purchased by Google.
Basically, Android is thought of as a mobile operating system. But it is not limited to mobile-only. It is currently used in various devices such as mobiles, tablets, televisions etc.
Android provides a rich application framework that allows us to build innovative apps and games for mobile devices in a Java language environment.
The Android open-source software stack consists of Java applications running on a Java-based, object-oriented application framework on top of Java core libraries running on a Dalvik virtual machine featuring JIT compilation.