What happens when an explosion begins

[oneswarm]

There is a saying that two kind of waves are generated when an explosion happens. one moves slow which can carry the object away .when someone fires with a pistol, the bullet is pushed by this kind of wave . the other is different , it move fast ,maybe at 8000m/s.
I wondered how this is possible. Can anyone explained it in a understanding way?
I only knows the basics about physics. and thanks for a little reference , for example ,some terminology which i can use to look up in wikepedia.

 

[aim1732]

Adiabatic heating of the air leads to an increase in the speed of successive waves that follow each other leading to a sharp edge and lumping of waves. These tend to constitute what are called shock waves.So you can look up shock waves, I guess.