What does the highest skill achieved on halo 3 mean?

[leggo my eggo]

You know when it says to get to the next promotion you need so many EXP points or highest skill achieved. What is the highest skill achieved?
and how do you get higher skills

 

[kewlguy77]

it means that its your highest level that youve gotten to playing matchmade games
like my highest level right now is a 22 in team slayer
the highest skill you can get is a 50 but its very hard
the way that you do this is buy winning matches and ranking up
but losing matches makes your level go down