What is the difference between S-waves and P-waves?

P-waves: These are also called primary waves. They move faster and are the first to arrive at the surface. The P-waves are similar to sound waves. They travel through gaseous, liquid and solid materials. 

S-waves: These are called secondary waves. They arrive at the surface with some time lag. They can travel only through solid materials.

Further Reading:

• Earthquake – Body Waves, Causes & Types
• Geography Notes