The vaporization that occurs below the surface of a liquid is called boiling.

Here's why:

* Boiling is a phase change where a liquid transforms into a gas.

* Evaporation is a similar process, but it happens at the surface of a liquid.

* Boiling occurs when the vapor pressure of the liquid equals the surrounding atmospheric pressure. This means that bubbles of vapor form within the liquid and rise to the surface.

So, while evaporation can happen anywhere in the liquid, boiling is specifically the process of vaporization happening within the liquid itself, causing the formation of bubbles.