Anions are simply ions that have acquired an extra electron, INCLUDING polyatomic ions. The extra electron gives it a negative charge.
Negatively charged polyatomic ions are called Anions.
Positively charged polyatomic ions are called Cations.
Polyatomic ions have 2 or more ions bonded together.
Most polyatomic ions are Anions, meaning they are negatively charged.
Some polyatiomic ions are Cations, meaning they are positively charged.
A fun way that I memorized it is that I love cats.
CATions are positive :)
List of common Polyatomic ions: