Anaerobic metabolism is a biological process in which energy is produced by cells without the use of oxygen. It occurs in certain microorganisms and in muscle cells during intense activity. In this process, glucose is broken down through glycolysis, resulting in the production of ATP and by-products like lactic acid or ethanol. Anaerobic metabolism is less efficient than aerobic respiration but allows survival in oxygen-limited environments. It plays a key role in fermentation and waste treatment. Microorganisms using anaerobic metabolism are essential in producing biogas and organic acids. This process supports various industrial and environmental applications.