A network switch in data transmission serves as a sophisticated device that connects multiple devices within a network, enabling them to communicate efficiently. It operates primarily at the data link layer, forwarding data packets between devices based on their MAC addresses. This targeted approach reduces network traffic by ensuring that data is sent only to the intended recipient rather than broadcasting it to all devices. Additionally, switches provide features such as traffic management and VLANs, enhancing overall performance and security within a local area network.