What are body waves?
Body waves are earthquake waves generated due to the release of energy at the focus. They move in all directions travelling through the body of the earth, hence the name 'body waves'.
There are two types of body waves called P-waves (primary waves) and S-waves (secondary waves). P-waves move faster and are the first to arrive at the surface. They can travel through gaseous, liquid and solid materials. S-waves arrive with some time lag and can travel only through solid materials.
The velocity of body waves changes as they travel through materials with different densities. The denser the material, the higher is the velocity.
Explanation
The answer is derived directly from the textbook context which defines body waves as waves generated at the focus that travel through the body of the earth. The context also explains the two types (P and S-waves) and their characteristics including velocity variations with material density.