S-waves, or shear waves, are a type of seismic wave generated by earthquakes. They move through the Earth by causing particles to oscillate perpendicular to the direction of wave travel. This characteristic makes S-waves slower than P-waves, or primary waves, which compress and expand the material they pass through. Unlike P-waves, S-waves cannot travel through liquids, which is why they are not detected in the outer core of the Earth. Their behavior helps scientists understand the Earth's internal structure and is crucial for studying seismic activity and predicting potential earthquakes.