Ionization is the process in which atoms or molecules gain or lose electrons, giving them an electrical charge. When electrons are stripped away, the remaining particles are positive ions. A gas containing free electrons and ions is called plasma.
Ionization matters in fields such as plasma physics, electronics, and cybersecurity. In a plasma demonstration, ionization explains how a gas can conduct electricity and produce a visible glow; it does not, by itself, show that nuclear fusion is occurring. In cybersecurity, the term can also describe ionizing radiation that may damage electronic components, though the specific risk depends on the radiation and equipment.