That says that if you claim that the thing being licensed violates your patents, your grant to their patents covering the thing is terminated. Facebook's patent grant has that, but also invalidates the patent grant if you claim that any of their patents are invalid (which you are likely to do if Facebook sues you for violating one of their patents).
So what if Apache committed something that is infringing on your patents and you sue? Does that mean you would have to stop using that specific apache licensed software (e.g. hadoop, maven, etc)
You lose the patent grant for that specific product: e.g. if you sue someone over a patent infringement in Hadoop you lose the patent grant for Hadoop, but not Maven. This may or may not mean that you have to stop using Hadoop.
