1. Pokémon. Previously called Stat Exp, they are attributes which give bonuses to a Pokémon's stats and improve differently depending on which Pokémon they defeat. These bonuses, in the form of effort points, are gained in addition to bonuses gained by increasing level. A Pokémon which increases in level using a Rare Candy instead of battling does not gain any EVs, making it weaker than a Pokémon who increases in level normally.
Roughly speaking, defeating fast Pokémon increases Speed better than fighting slow Pokémon, defeating Pokémon with high hit points improves HP more than defeating Pokémon with low HP, and so on.
Unlike experience points, which are reduced when multiple Pokémon are receiving experience, effort points are awarded equally to all Pokémon who participated in defeating a Pokémon. Though they are shared, each of the Pokémon will receive the standard amount of effort points.
There are several ways to manipulate EVs and they have changed over time.
2. Opinion. Something that only the most hard core of hard core Pokémon players worry about and even know about; a huge time suck.
IV [ahy-vee] / individual values [in-duh-vij-oo-uhl]
1. Pokémon. Sometimes called Determination Values (DVs for short), are the Pokémon equivalent of genes. They are instrumental in determining the stats of a Pokémon, being responsible for the large variation in stats among untrained Pokémon of the same species.
2. Opinion. Pokémon's meta-game drives me to drink Miltank Milk and Vodka.
EX. Basically, someone sat down at Game Freak and said, "How can we create something that most children could hardly understand or care about, but would drive many older players to madness with the monotony of grinding for the perfect Pokémon?"
Someone put up their hand and with a demonic chuckle answered, "EVs and IVs. Like all Pokémon give off special bonuses and all Pokémon have unique DNA."