1) An atom or group of atoms that have a positive or negative electric charge due to a gain (negative charge) or loss (positive charge) of one or more electrons. Atoms with a positive charge are known as cations; those with a negative charge are anions.

2) An atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons.

3) A charged subatomic particle (as a free electron).