Ethernet is a system for linking computers so they can share files, printers, and a connection in the same building or on the same local network. In daily talk people mostly mean the cable with a little clip that clicks into a laptop or a wall socket, and the boxes and ports that go with it. Shop staff and office IT people use the word all the time; it is technical, but not rare or fancy. Though actually, Ethernet is not the same as the internet. Ethernet is usually the local setup in one place. The internet is the huge public network those local setups join. Wi-Fi does a similar local job without a wire, so people stretch “Ethernet” to mean “the wired kind, not Wi-Fi.” The name began as a Xerox trademark. The picture was that messages would move through the network the way older science imagined light moving through “ether,” an invisible stuff filling space. Today it is a normal common noun, though you still often see a capital E.