Stands for "Network Basic Input/Output System." NetBIOS was introduced in 1983 by IBM as an improvement to the standard BIOS used by Windows-based computers. The BIOS provides an interface between the computer's operating system and the hardware. As the name implies, NetBIOS adds support for networking, including the ability to recognize other devices connected to the network.
NetBIOS provides an API (Application Program Interface) for software developers to use. The NetBIOS API includes network-related functions and commands, which can be incorporated into software programs. For example, a programmer can use a prewritten NetBIOS function to enable a software program to access other devices on a network. This is much easier than writing the networking code from scratch. In other words, NetBIOS prevents programmers from having to "reinvent the wheel" just to get their program to connect to a network.