Short for Android Package File, an APK is the file format which stores applications developed for the Android operating system. These files can be downloaded from the Google Play store, or manually installed using an Internet browser. APK files can be opened by an Android smartphone or tablet, a Chromebook with the Google Play store enabled, or a computer running an Android emulator.
Android apps are usually developed in Android Studio, using Java, the official coding language supported by Android. However, other languages are supported by the Google Play store, including Kotlin, C++, C#, and BASIC.