A switch is a Data Link layer networking device that connects multiple devices within a LAN and forwards frames selectively — only out the specific port leading to the destination MAC address — rather than broadcasting to every port like a hub does.

It builds and maintains a MAC address table by learning the source address and incoming port of every frame it sees, allowing it to make intelligent per-frame forwarding decisions. This reduces unnecessary traffic, eliminates collisions (each port is its own collision domain), and allows multiple simultaneous conversations on different port pairs at once (full-duplex operation).