It is used in medical terminology to describe the presence or absence of carbon dioxide in the blood or body.
Here are some examples:
* Hypercapnia: High levels of carbon dioxide in the blood.
* Hypocapnia: Low levels of carbon dioxide in the blood.
* Acapnia: Absence of carbon dioxide in the blood.
It's important to note that "acapnia" is rarely used in medical practice as it's essentially impossible to have zero carbon dioxide in the blood.