Here's how it works:

* Sediment Deposition: Over time, layers of sediment accumulate, one on top of the other.

* Weight and Pressure: The weight of the overlying sediment layers exerts immense pressure on the layers below.

* Compaction: This pressure forces out water and air from the spaces between sediment grains, causing them to pack together more tightly.

* Lithification: Compaction, along with cementation (the precipitation of minerals between grains), is a key part of the process called lithification, which transforms loose sediment into solid rock.

So, compaction is the process where the weight of sediment above squeezes and compresses the sediment below, reducing the pore spaces and ultimately contributing to the formation of sedimentary rocks.