Server Message Block (SMB) is a network protocol used for providing shared access to files, printers, and other communication between nodes on a network. It is a client-server communication protocol, where clients request services and servers respond to those requests. SMB operates at the application layer of the OSI model and facilitates communication between devices running different operating systems. With the introduction of SMB3 and improvements in subsequent versions, the protocol has become more efficient, secure, and feature-rich, making it suitable for various network file-sharing scenarios.