An ion is an atom or molecule that has a net electrical charge. An ion is formed after taking one or more electric charges by means of loss (positive ions or cations) or acquisition (negative ions or anions) of one or more electrons.
Positively charged ions are called cations (e.g. \(\textrm{Na}^+\), \(\textrm{NH}_4^+\)) while negatively charged ions are called anions (e.g. \(\textrm{Cl}^-\), \(\textrm{CO}_3^{2-}\)).
Ionization
Ionization (or ionisation in British English), is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes.