The phrase references installation files typically associated with the Android operating system, used to install applications. It is a file format incompatible with Apple’s mobile operating system and its devices. Such a file cannot be directly installed on an iPhone, iPad, or iPod Touch.
Understanding the discrepancy is important because it highlights the fundamental differences between the two dominant mobile platforms. The Apple ecosystem utilizes a different file type for its applications and employs a closed environment restricting software installations from outside its official App Store without specific developer privileges or jailbreaking the device.