Learn in the textbookConnecting Devices That Make Up a Network
DefinitionA switch (スイッチ), or Layer 2 switch, is a concentrator that reads the destination MAC address of incoming data and forwards it only to the port where that device is connected.
ExplanationA MAC address (MACアドレス) is an ID number assigned at manufacture to each network component. A switch records each incoming frame's source MAC address and port in a table, then uses that table to work out which port leads to the destination. In this unit a plain "switch" means this Layer 2 switch, while one that decides where to send data by IP address (IPアドレス), the number assigned to devices on a network to tell them apart, is called a Layer 3 switch (レイヤ3スイッチ).
AnalogyIt is like a mailroom clerk who reads the name on each envelope and drops it only in that person's slot.
Memory hookTo switch means to change over.