Yeah, it is defined at the bottom of the file:

> A "Necessary Claim" is a claim of a patent owned by Facebook that is necessarily infringed by the Software standing alone.

So when they say "license under any Necessary Claims" they are granting a patent license, the copyright license in the LICENSE file is separate.

The FAQ link provided by silentstreet makes it very clear:

> Does termination of the additional patent grant in the Facebook BSD+Patents license cause the copyright license to also terminate? > > No.