It means training in certain places hat has Pokemon that if you defeat them,will give you EVs.Some people go to certain places for certain EV like speed or defence beacause they want there Pokemon's stat to improve.Like,in B or W 2,if you wanted to strengthen your Pokemon's defence,you would train in a cave like reversal mountain beacause most rock and steel types are found there and can give a lot of defece EVs.
Important information for EV Training:
- You can only go up to 252 EVs in any one Stat, and you only have a total of 510 Evs you can invest into one Pokemon.
- Certain Pokemon give off certain EVs and the pokedex pages on this site tells you which Pokemon gives which EVs.
- You can use items to increase the Evs you gain, increase the Evs directly(the stat increasing items are: Carbos,Protein,Iron,Calcium,HP Up,Zinc) , and you can use certain berries to decrease Evs if you placed some you didnt mean too.
- Pokemon that catch the Pokemon Virus Pokerus gain more Evs during and after they are infected with the Virus.