Final answer:
APK stands for Android Package Kit, which is the file format used by Android for app distribution. The four main Android components are Activities, Services, Broadcast Receivers, and Content Providers.
Step-by-step explanation:
APK stands for Android Package Kit. It is the file format used by the Android operating system for distribution and installation of mobile apps and middleware. APK files are a type of archive file, specifically, in zip format packages based on the JAR file format, with .apk as the filename extension.
The main components of the Android operating system include Activities, Services, Broadcast Receivers, and Content Providers. These four components are key to the Android application model and each serves a distinct purpose in an Android app, providing a distinct way to create apps with different behaviors.