Hardline is a type of material that is used for transmitting things like signals or information. It is usually made up of a long, thin copper wire that is covered in a protective sheath to keep it safe.
Think of your phone charger cord - it is made of a long, thin wire that you plug into your phone to charge it up. Now imagine that wire is much longer and thicker, like a garden hose, and covered in a protective layer. That is what a hardline looks like.
Hardline wires are used to transmit things like television signals, radio signals, and even internet signals to your home. They can be buried underground or strung up on poles, but they have to be carefully protected to make sure nothing interrupts the signal.
When you watch TV, listen to the radio, or use the internet, the information is sent through the hardline to your house where it is decoded by your TV or computer.
So really, hardline is like a long, special cord that brings us all the things we love to watch and listen to!