From a press release from Intel:
Thunderbolt Networking, emulating an Ethernet connection environment, provides a 10GbE data exchange between two computers. Now available on Macs with OS X Mavericks, a PC driver will soon make it possible to connect two PCs or a PC to a Mac, adding a new level of flexibility for media professionals. By offering simple and fast file sharing, Thunderbolt Networking allows backup or upgrade via two computers like never before, using existing cables and connectors.
Almost a year after launching Thunderbolt 2, Intel is now back with this new feature already available on OS X Mavericks: the possibility for you to connect two Macs with a Thunderbolt cable and exchange data between them as if they were on a network 10 -Gigabit Ethernet. Very good! (Macworld)