A highly compressed game is a file package that has been reduced in size using advanced compression algorithms (like ZIP, RAR, or 7z).
How to Download & Install Mortal Kombat X Highly Compressed (Offline)
Download Mortal Kombat X Offline For Android Highly Compressed: The Ultimate Guide
Therefore, an "Offline" version implies a cracked, modified, or pirated iteration of the game files—a "Mod APK."