It doesn't define a protocol. NetBIOS over TCP/IP provides the NetBIOS programming interface over the TCP/IP protocol. It extends the reach of NetBIOS client and server programs to the wide area network (WAN). It also provides interoperability with various other operating systems.

Is NetBIOS over TCP IP needed?

Yes. To improve performance, it's recommended that you disable NetBIOS over TCP/IP on your cluster network NIC and other dedicated-purpose NICs, such as for iSCSI and Live Migration.

Why would you use NetBIOS?

NetBIOS is an abbreviation of Network Basic Input/Output System. The primary purpose of NetBIOS is to allow applications on separate computers to communicate and establish sessions to access shared resources, such as files and printers, and to find each other over a local area network (LAN).