An APK (Android Package Kit) is the file format used for installing apps on Android devices. It contains all essential components like code, resources, and a manifest file. APKs allow users to install apps manually, bypassing the Google Play Store. Developers use them for testing before public release. However, downloading APKs from untrusted sources can pose security risks like malware. To install an APK, users must enable "Unknown Sources" in settings. APKs also provide access to beta versions and modded apps.
