The document defines computer networks and network topologies. It discusses local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs). It also covers different network topologies including bus, star, ring, mesh, and tree. LANs are used for communication over short distances like within an office building. MANs span a larger area like a city and consist of interconnected LANs. WANs are used for long distance communication over large geographic areas. The star topology connects all devices to a central hub. The bus topology uses a common backbone cable that connects all nodes. The ring topology connects each node to the two nodes on either side, forming a closed loop.