Pokémon Trading Card Game
If a Pokémon's Element has a strength against another Element, then the Pokémon's attack will take away twice as much HP as the attack's normal attack power. Likewise, if a Pokémon's Element has a weakness against another Element, then the Pokémon will lose twice as much HP if it is attacked. For example,  a Electric-Type Pokémon's strength is Water, which means that a Water-Type Pokémon's weakness is Electric. Therefore, if a Electric-Type Pokémon attacks a Water-Type Pokémon with an attack that takes away 30 HP, then the attack will take away 60 HP from the Water-Type Pokémon because of the Electric-Type's strength over Water. If an Element has resistance, then certain Elements will not take away any HP. For example, many Fighting-Type Pokémon have resistance to Electric-Type Pokémon, which means that attacks from Electric-Type Pokémon cannot take away any HP from those Fighting-Type Pokémon.