Server Message Block 2 - SMB2
Short for Server Message Block 2, SMB2 is a file transfer protocol commonly used by network-attached storage (NAS) devices and file servers for sharing files and data. SMB2 first debuted with the release of Microsoft's Windows Vista in 2007 as a successor to the original SMB protocol, and it's now supported by Mac OS X (as of the OS X Mavericks release), Linux and Samba as well.
The SMB2 protocol offers better performance and increased security over the original protocol. Apple made the switch to SMB2 in the Mavericks release after moving from its own proprietary SMBX protocol, which Apple had developed to replace the aging AFP (AppleTalk Filing Protocol) file sharing protocol used by the company since the 1980s.