OSI stands for Open Systems Interconnection. It is a reference model that enables interconnection between different applications in networks. The model has 7 layers: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer.
The first - the physical layer and the second data link layer, the network layer is associated with common networks (e.g. Ethernet LANs). The IEEE standard 802.2 describes the physical layer, while the standard 802.3 the second layer.