NetBIOS stands for Network Basic Input/Output System. It is a networking protocol that allows applications on different computers to communicate within a local area network (LAN). Originally developed for IBM's PC Network, it provides services related to the session layer of the OSI model, enabling file and printer sharing among devices. NetBIOS operates over various transport protocols, including TCP/IP and NetBEUI. It uses names to identify devices on the network, allowing users to access resources easily. While it has been largely replaced by more modern protocols, it is still used in some legacy systems and applications.