An APK (Android Package Kit) is the file format used to distribute and install applications on Android devices. It contains all necessary components like code, resources, assets, and certificates required for an app to function. APK files are similar to EXE files on Windows and can be installed manually outside the Google Play Store. Users can download APKs from third-party sources, but caution is advised to avoid security risks like malware. Developers use APKs for testing apps before official release. Modded APKs offer extra features but may violate terms of service. Always verify sources before installing an APK file.
