The process of releasing energy without the use of oxygen is called anaerobic respiration, or anaerobic metabolism. It is also termed [[1]]. 

Anaerobic respiration is the process of releasing energy without the use of oxygen. It is also known as anaerobic metabolism or fermentation. 

It happens in cells that don't get enough oxygen, like those in muscles during intense exercise. 

Lactic acid fermentation, which produces lactic acid as a byproduct, is the most common type of anaerobic respiration in animals. 

When oxygen is unavailable, this type of fermentation is used as a temporary source of energy, allowing cells to continue producing energy even in the absence of oxygen.