Broadband is an internet term that does what it says on the tin. It uses a broad band of frequencies to carry a signal, traditionally through phone line wires. When someone calls you on a phone, the sound travels through wires at a very low frequency. However, phone wires are designed to carry much higher frequencies. This can be due to the improvement of technology like directional couplers.
This is often due to how phone lines are made, but since phone lines can handle a lot more frequency than is used for a traditional phone call, the line also carries other data. All this data has in common is that it runs on higher frequencies than the call, so nothing is interrupted. This large band of frequencies is why it is called broadband.
The wires also have something called a margin, which is a section of power that is never used. Think of it like only using 90% of something, while saving the other 10% for emergencies. That’s what a margin is, and having that extra margin often stops re-syncs, where the phone or internet stops to readjust to the full usage of power.
Depending on the factors that the line is in, such as their weather, the temperature around the room, and the interference in the line, the margin can be very large or very small. The margins are almost always monitored and adjusted when margins change based on the environment. That way if the margin does get to be too large for the line, adjustments can be made without having to stop a customer’s usage of the service.
So while it might be tempting to think of broadband as another way to say fast internet, it is much much more than that when it comes to how signals work.