STAB = Same Type Attack Bonus - If a Pokémon uses an attack that matches one of its types, this bonus factor is equal to 1.5; otherwise this is 1. An example of that is salamence with aerial ace, a flying attack for a flying type where instead of being a 60 power, it's a 90 power.
Sweeper is usually a fast with either high attack or special attack that can defeat most pokemon types. example is starmie with surf, ice beam, thunderbolt & psychic.