A process that does not require oxygen is known as anaerobic. This term is often used in the context of biological processes, such as anaerobic respiration or fermentation.
In anaerobic respiration, organisms convert energy from nutrients without using oxygen. For example, some bacteria and yeast perform fermentation, which produces energy, as well as byproducts like ethanol or lactic acid, depending on the specific pathway used. Anaerobic processes can occur in environments devoid of oxygen, such as deep in soil, in water sediments, or in the digestive systems of certain animals.