Question

I don't know what is it

Answer 1

It is PokeRus.
PokeRus doubles EV gains. You can spread it, and Pokemon can only have it for a few days, unless it is in the PC.

http://bulbapedia.bulbagarden.net/wiki/Pokerus

Comments

My drapion have it from Pokemon platinum to heart gold to white and it doesn't go away

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Cool. You can click the check mark by my answer, it really helps.

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Thanks for the information

Answer 2

PkRs is short for pokerus. It is a virius but it is actully helpful because it doubles the evs you get after every battle

Answer 3

PKRS means PokeRus, its where any pokemon who has it gains EVs faster. The ability to spread it goes away after sometime but it will always keep the effects from PokeRus.

Source-Personal Experience