The louder a sound, the more energy it has. This means loud sounds have a large amplitude. Think about what an amplifier does: it makes sounds louder. It is the amplitude that relates to how loud sound is.
Scroll down to related links and look at "Sound volume".
Acoustic energy is sound energy.
The definition of sound says that it is a disturbance of energy that comes through matter as a wave, and that humans perceive sound by the sense of hearing.
Sound pressure is the effect and sound power (energy) is the cause.
Scroll down to related links and look at "Sound pressure and Sound power - Effect and Cause".
But our eardrums are only sensitive to the sound pressure, and so are microphone diaphragms. Think of sound pressure level meters (SPL meters).
So better ask: What is sound pressure?
Scroll down to related links and look at "Sound pressure - Wikipedia".