The Android operating system (OS) is based on the Linux kernel. Unlike Apple's iOS, Android is open source, meaning developers can modify and customize the OS for each phone. Therefore, different Android-based phones often have different graphical user interfaces GUIs even though they use the same OS.
Android phones typically come with several built-in applications and also support third-party programs. Developers can create programs for Android using the free Android software developer kit (SDK). Android programs are written in Java and run through a Java virtual machine JVM that is optimized for mobile devices. The "Dalvik" JVM was used through Android 4.4 and was replaced by Android Runtime or "ART" in Android 5.0. Users can download and install Android apps from Google Play and other locations.
If you are unsure what operating system your phone or tablet uses, you can view the system information by selecting "About" in the Settings menu. This is also a good way to check if your device meets an app's system requirements. The name "Android" comes from the term android, which is robot designed to look and act like a human.