Heavy water, or deuterium oxide (D₂O), is a form of water where the hydrogen atoms are replaced with a heavier isotope called deuterium. This makes heavy water denser than regular water, which consists of hydrogen (H₂O). Heavy water is used in various scientific applications, including nuclear reactors, where it acts as a neutron moderator. In addition to its use in nuclear technology, heavy water is also utilized in certain types of chemical research and biological studies. While it is not toxic, consuming large amounts can be harmful due to its effects on biological processes.