STAB (stands for Same-type attack bonus) is a boost in the base power of a move that has the same type as the Pokémon using the move. This boost increases the damage done by 50%. This boost can become 100% instead when a Pokémon has Adaptability as its natural Ability.

For example, a Fire-type Pokémon using a Fire-type move will gain a 50% boost because the attack is the same element as a Pokémon. STAB does not apply to moves that do a set amount of damage nor ones that do not use the normal damage formula, such as Dragon Rage and Seismic Toss.

Misconceptions

Hidden Power

Contrary to popular belief, Hidden Power does, in fact, receive STAB as well if the Hidden Power's type is the same type as the Pokémon.

Normal-type Pokémon

Normal-type Pokémon also receive STAB, contradicting some of Nintendo's strategy guides.

Dual-type Pokémon

Dual-type Pokémon also receive STAB if the move type is the same to one of their types. Therefore, a Pidgey will receive STAB from Aerial Ace and Tackle.