S Waves, or secondary waves, are a type of seismic wave that move through the Earth during an earthquake. They are slower than P Waves and can only travel through solids, not liquids or gases. S Waves move in a side-to-side motion, which can cause significant shaking and damage to structures on the surface. When an earthquake occurs, S Waves follow the initial P Waves, arriving at seismic stations later. Their ability to only travel through solid materials helps scientists understand the Earth's internal structure, including the presence of liquid layers like the outer core, which cannot transmit S Waves.