To understand exactly what this download entails, it helps to look at the specific terms:

Legitimate distributors often provide a "hash" (a unique string of characters) that allows users to verify that the file they downloaded hasn't been tampered with.

(such as those from FitGirl, ElAmigos, or specialized adult game sites) is a compressed version of the game designed to: Reduce Download Size : Highly compressed files save bandwidth. Include Pre-installed Mods

Standard Android installers may fail for some versions, requiring the use of XAPK Installer tools to correctly unpack components.