What term describes a particle that is electrically charged, either positive or negative?

The term that describes a particle that is electrically charged, either positive or negative, is "ion." Ions are formed when atoms gain or lose electrons, resulting in a net electrical charge. A positively charged ion is called a cation, while a negatively charged ion is referred to as an anion. This distinction is important in various chemical reactions and processes, as ions play a critical role in electrical conductivity, bonding, and the formation of compounds.

The other terms do not describe charged particles. An atom is the smallest unit of an element and can be neutral if it has an equal number of protons and electrons. A molecule consists of two or more atoms bonded together and is typically neutral as well. An isotope refers to variants of a particular chemical element that differ in the number of neutrons in the nucleus, resulting in different atomic masses but not necessarily a charge.