The document discusses the OSI model, which is a standard reference model for how information is transferred between applications running on different computers over a physical medium. It describes the seven layers of the OSI model - physical, data link, network, transport, session, presentation, and application layer - and provides details on the functions of each layer, such as how the physical layer handles data transmission and the data link layer performs error correction. It also lists example protocols like HTTP and SMTP that operate at the application layer.