An Archetype is a group of cards with at least 1 defining property.
Archetypes are often identified by a term appearing in all its members names, e.g. "Elemental Hero" or "Morphtronic". Support cards for the archetype usually reference cards with that term in their name e.g. "Elemental Recharge".
The concept of archetypes is often used in the manga and anime series to define a character's personality, look, state of mind or style of play.