(swich) (n.) (1) In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs.
(3) Another word for option or parameter — a symbol that you add to a command to modify the command’s behavior.
See also Webopedia’s “Did You Know… Routers, Switches and Hubs: What’s the Difference?”