What is the difference between a cation and an anion?

Normally atoms are neutrally charged because they have the same number of electrons (negatively charged particles) as protons (positively charged particles). Sometimes due to biological processes, radiation, or other effects, atoms may gain or lose electrons in their outer shells. This creates an imbalance of charge in the atom, which we then refer to as ion.

Cation is an atom that has lost an electron, thereby having a net positive charge.

Anion is an atom that has gained an electron, thereby having a net negative charge.

You can easily remember them with a mnemonic device:

Cation is a pawsitive ion.

Anion is a negative ion.