APK. 1 file is the extension of the APK (full name: Android Application Package) file used by the Android operating system. This is a common form of software distribution used to install and run applications on mobile devices. The number after the "." symbol usually represents the name or version number of the APK package.

APK files are the standard file format for installing and running applications on the Android operating system. It is a compressed package that contains all the files and resources required by the application, including code, resources, images and other necessary files.

An APK file is similar to an EXE file on a Windows system or a DMG file on a Mac system. It is an installation package for an application. When you download an app from the Google Play Store or other sources, you usually download an APK file. You can install it by clicking on the APK file and following the prompts, or using the file manager on your Android device to move the APK file to the device and open it for installation.

The extension of the APK file is .apk, and numbers or letters are usually added after the file name to distinguish different versions or copies. An APK file usually contains the application's main code, resources, libraries, and other necessary files, which are packaged into a single file.

Functions of APK files:

1. Install the application: The APK file contains all the files and resources required by the application and is the installation package of the application. The app can be installed on your Android device by clicking on the APK file and following the prompts to install it.

2. Update applications: APK files can be updated manually, and users can update applications by downloading new APK files and installing them. This gives users more flexibility in controlling application updates.

3. Uninstall applications: Installed applications can be deleted by uninstalling APK files.

4. Expand application functions: APK files support custom functions and plug-ins, which makes the application more flexible and scalable. New functionality or features can be added to existing applications by developing plug-ins or using third-party libraries.

5. Protect application security: APK files are signed and encrypted to ensure their integrity and security. Only applications with the correct signing key can install and run. This helps prevent malware or unauthorized applications from accessing the user's device.

Reference for the above content: Baidu Encyclopedia-APK