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. \(\textrm{Cl}^-\), \(\textrm{CO}_3^{2-}\)).