Nature

A Pokémon's Nature usually affects the value of two of its stats, ultimately increasing one of its non-HP stats (Attack, Defense, Special Attack, Special Defense, or Speed) by 10% and decreasing another by 10%.

Every Nature represents one of the 25 unique possible combinations of stat increase and decrease; thus, there are five Natures that have no effect on the Pokémon's stat growth as they technically increase and decrease the same stat (Bashful, Docile, Hardy, Quirky, and Serious).