Effort Value

Attributes which give bonuses to a Pokémon's stats and improve differently depending which Pokémon they defeat. These bonuses, in the form of effort points, are gained in addition to bonuses gained by increasing level. Pokemon who are candied do not receive these bonuses, making them weaker than those leveled by battling.

Trainer 1: I worked really hard, but my Charizard's speed Effort Value is still low!

Trainer 2: That's because Charizard's base speed is already low. It's attack should be higher, but it's nature can affect it's stats, too.