NetBEUI stands for NetBIOS Extended User Interface and is pronounced net-BOO-ee.
It is a new extended version of the original NetBIOS protocol and adds additional specifications to the protocol. NetBEUI was developed by IBM, but has been adopted by Microsoft, Hewlett-Packard, and DEC.

Despite What some people think NetBEUI is not routable. Oh, it will eventually encapsulate the packet and pass the router, but not before making a lot of noise first. Forcing his Users to log on to his NT file server across subnets is the real reason the network seems slow, not the new Cabletron switches.

No, it is not routable, however that is one of it's advantages. If you are host to some mission critical data, you can set NetBeui up on the private side if your router, and no one can see it. It's an invisible network, to outsiders. Another disadvantage hoewever, is that it is also undetectable to the rest of your WAN (if you have one).