Seismic waves are categorized as mechanical waves, which travel through the Earth's materials. They are produced by geological phenomena, such as earthquakes, and can be classified into two main types: P-waves (primary waves) and S-waves (secondary waves). P-waves are compressional waves that travel faster and through solids and liquids, while S-waves are shear waves that only move through solids, providing valuable insights into Earth's internal structure.