The primary characteristic of anaerobic organisms is their ability to thrive in environments devoid of oxygen. These organisms, which include many bacteria and archaea, utilize alternative metabolic pathways to extract energy from organic materials through processes like fermentation. Anaerobic organisms play crucial roles in various ecological processes, such as the decomposition of organic matter and nutrient cycling. They are also significant in industrial applications, including waste treatment and biofuel production, highlighting their importance in both natural and engineered systems.