Charge density wave

Charge density wave is a pattern of electric charge (like an ocean wave) that moves back and forth in a solid material. Imagine a playground filled with people. All of the people are standing in a line five feet apart (a "wave" of people). Then a whistle is blown and everyone takes five steps in one direction and stops. A few seconds later, another whistle is blown, and everyone takes five steps back and stops. This is like a charge density wave: the people represent the electric charge moving in a repeating pattern like waves.