STAB: STABis a abbreviation for same type attack bonus, the 1.5x boost Pokemon's attack receives when the attack and the Pokemon are if the same type. It is used to describe the boost itself as well as moves that get the boost. For example, sandslash is a ground type, so when it uses ground type moves like earthquake they are one and half times as powerful as normal. As such, earthquake is Sandslash's STAB, and Sandslash gets STAB on earthquake.
Sweepers: sweepers in general are offensively oriented Pokemon whose sole purpose on a team is to take out the opponents team. They are different from wallbreakers and other offensive roles in competitive teams in that they are designed to take out an entire team, rather than specific Pokemon. Most sweepers run a stat boosting move, such as calm mind or dragon dance, in order to facilitate a sweep, and need the support of teammates to remove Pokemon that counter them. Pokemon such as lucario and volcarona commonly run sweeper sets. There are multiple kinds of sweeper. sweepers are typically categorized into physical, special and mixed, and each runs physical stacks, special attacks and both respectively. Types of sweeper include setup sweepers, who sinpky just use a stat boosting move to sweep, weather sweepers like Victreebel , who rely on a weather condition to augment their ability, and bulky sweepers, who rather than rely on speed rely on their good defensive stats and attacking ability to sweep.
Evs: evs, short for effort values, boost a Pokemons individual stat. A Pokemon can only have 255 in each stat and can only have 508 total. It should be noted that evs only effects a stat in multiples of four. As such 252 evs gets the same result as 255 evs. Battling certain Pokemon gives your Pokemon certain evs, as do vitamins and wings.
Here are some helpful links
http://bulbapedia.bulbagarden.net/wiki/Same-type_attack_bonus
http://bulbapedia.bulbagarden.net/wiki/EVs
http://www.smogon.com/dp/articles/pokemon_dictionary
