What is the correct definition of a compression?

Compression - "Compression is a process in which the actual space covered by any sort of entity is reduced and the values of the given parameters are lowered."

Explanation:

Definition with respect to Stress and strain - "The change in actual length, L to a new length,ΔL due to applied stress is called as compression".

Definition with respect to longitudinal wave - "The region of the wave where the particles present are more close to each other is called as compression".

The answer that I found is ...

Compression. A compression is a region in a longitudinal wave where the particles are closest together. Rarefaction. A rarefaction is a region in a longitudinal wave where the particles are furthest apart.