The process when an atom loses or gains one or more electrons is called ionization. When an atom loses electrons, it becomes a positively charged ion, or cation, while gaining electrons results in a negatively charged ion, or anion. Ionization occurs through various processes, including chemical reactions, exposure to radiation, or thermal energy. This phenomenon is fundamental in chemistry and biology, as the formation of ions significantly influences chemical bonding, reactivity, and interactions between atoms and molecules in biological systems.