Deuterium is a stable isotope of hydrogen, with an extra neutron in the nucleus. It is commonly used in research areas such as nuclear physics, astrochemistry, and nuclear fusion. Deuterium is also utilized in medical research, specifically in studying metabolic processes and developing new drugs. Additionally, deuterium is a key component in the study of paleoclimatology, as the ratio of deuterium to hydrogen in water samples can provide insights into ancient climate patterns.