Isotopes are atoms of the same element that have different masses due to the number of neutrons in their nucleus. They are commonly used in various fields such as nuclear medicine, geology, and biology. Synonyms for isotopes include atomic varieties, isotopic forms, isotopic species, nuclides, radioactive isotopes, and stable isotopes. These terms help to specify the type of isotope being referred to and their properties. For example, radioactive isotopes are those that emit radiation due to unstable nuclei, while stable isotopes have a fixed number of neutrons in their nucleus and can be used for isotope analysis in forensic science and environmental studies.