Dissolved oxygen is a crucial element for aquatic life. It is the amount of oxygen that is present in the water and is used by aquatic organisms for respiration. There are many synonyms for dissolved oxygen, including oxygen saturation, dissolved air, and oxygen content. Oxygen saturation refers to the amount of oxygen that is dissolved in the water in relation to the amount that is required to completely saturate it. Dissolved air is the amount of air that is dissolved in the water. Oxygen content refers to the amount of oxygen that is present in the water, and it is generally measured in parts per million (ppm). These synonyms are all important when determining the health of water ecosystems.