Modern AAA games like Call of Duty: Ghosts are massive (often 30GB+). To make downloading or sharing easier, they are frequently split into smaller segments (Part 1, Part 2, etc.).
Here is a write-up explaining what this file is, how to handle it, and what to keep in mind regarding the game itself. What is this file?
Instead of the traditional "Zombies" mode found in Black Ops, Ghosts featured an alien-defense mode called Extinction.