Compression is the part of a medium where particles are closer together than they are in the rest of the medium.

Here's why:

* Compression refers to the act of squeezing or pressing something together.

* In a medium, like air or water, the particles are constantly moving.

* When a wave travels through the medium, it causes the particles to bunch up in certain areas and spread out in others.

* The areas where the particles are closer together are called compressions.

Think of it like a spring: When you push on one end, the coils of the spring get closer together. This compressed area then travels down the spring as a wave.