Once upon a time, long, long ago, people used to connect their computer to another computer using a device called a modem.
This modem would “modulate” the digital information from their computer into an analog signal that was sent over an analog telephone network to another modem at the other end of the phone call.
The modem on the other end of the call would then “demodulate” the analog signal back into digital information and pass it on to that computer.
That, folks, is why they called it a “modulator-demodulator” – or “modem” for short.
Back and forth this modulation and demodulation of data would go, in what could only be described as a slow and noisy process (good thing we only had to listen to the modems “shaking hands” and not the entire modulated conversation!).
Then, one day, people were able to get a digital line to their houses! No longer would they need the squeak and squawk of modems modulating and demodulating digital data to and from analog lines.
But these connection weren’t Ethernet connections, they were ISDN, digital subscriber lines (or “DSL) or cable, or something else. We couldn’t just plug our Ethernet cable into the cable’s coax or DSL’s RJ-11… We had to do something to bridge the Ethernet connection from our computers to the ISP’s network… we had to have some sort of a device to do this… but it didn’t modulate or demodulate anything. It was just changing one digital signal into another digital signal. It was bridging the gap between these two types of networks… what was that magical device called?
Not a “cable modem.” Not an “ISDN modem.” Not even a “DSL modem.” Oh, that’s right, it's called a BRIDGE!