In Clone Hero, a highway refers to the layout of the notes on the screen. It's the path that players follow as they press the corresponding buttons on their guitar controller. By default, Clone Hero comes with a set of pre-defined highways, but these can get repetitive and limit the overall gameplay experience. That's where custom highways come in.
If you prefer movement on your fretboard, Clone Hero supports video highways, though they require a specific setup: custom highways for clone hero