A device used to connect multiple computers in a network is called a switch. Switches operate at the data link layer (Layer 2) of the OSI model, facilitating communication between devices within the same local area network (LAN). They efficiently direct data packets to the intended device based on MAC addresses, reducing network congestion and improving overall performance. Unlike hubs, which transmit data to all connected devices, switches intelligently send data only to the specific device that needs it. This increased efficiency helps improve speed and reliability in network communications.