Dang, it's ahrd to get a 4 player match going...
Ahh, ok.
IVs are (prior to breeding) totally random values ranging from 0 to 31 in each of the stats.
The higher the value (through 31), the higher your Pokemon's final stats will be, which when combined with your Nature and your EVs, can lead to much higher final values.
Like when you check out Serebii's stats (Max, Min, Beneficial, and so on), you'll see how drastic the changes can be.
As I said, you initially have no control over your IVs, but when breeding, it's much easier to spread good IVs down with items like Destiny Knot and Power items.