STAB (an abbreviated form of Same-type attack bonus) amplifies a move's power when a Pokémon's type matches the move's type. This boost in power is increased by 50%. So if a fire-type Pokémon uses Ember, which is a fire-type move, Ember's base power is changed from 40 to 60. If a Pokémon has Adaptability, the boost in power is increased by 100% instead. So if Ember was used in this case, its base power will change from 40 to 80. 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.
Normal-type Pokémon also receive STAB, contradicting some of Nintendo's strategy guides.
Dual-type Pokémon also receive STAB if the move type is the same to one of their types. Therefore, a Pidgey (a Normal/ -type) will receive STAB from Aerial Ace (a -type move) and Tackle (a Normal-type move).