According to the USA Today, co-developers Infinity Ward and Sledgehammer Games are beefing up the Spec Ops mode with online matchmaking, leaderboards, and a separate progression system from multiplayer. The centerpiece of the renovation, however, is a new Horde-like Survival mode that takes place on the multiplayer maps.
As you would expect, players face off against unlimited waves of increasingly difficult enemies. The map USA Today played, called Dome, featured a "Cold War-era desert radar command bunker" and some creative new enemies like suicide bomber dogs that explode a few seconds after you put them down. When the waves become too much to suppress with your **** rifle, you can use in-game currency to purchase defensive enhancements like turrets.