Nitrogen-fixing bacteria are microorganisms that have the natural ability to convert atmospheric nitrogen into forms that are usable by plants. These bacteria play a crucial role in improving soil fertility and sustaining plant growth. There are various synonyms for nitrogen-fixing bacteria, including diazotrophs, nitrogenase-positive bacteria, and nitrogen-fixing microorganisms. Diazotrophs are microorganisms capable of fixing atmospheric nitrogen through biological nitrogen fixation, and this includes nitrogenase-positive bacteria. Nitrogen-fixing microorganisms are another term used to describe these bacteria and refer to all microorganisms that can fix nitrogen. All these synonyms emphasize the vital role of these bacteria in plant health and soil fertility.