Formal language used by prestigious people
Informal language, slang, vernacular, regional dialects
The language spoken by the earliest settlers of America
Hey dude lets go chill at the crib.
Where did I place my car keys?
Did you see the lights on that Christmas Tree?
I'm goin to the jumpoff up on East Saratoga Street, you down?
When I came home yesterday, someone's car was parked in my space.
Whole time, nobody saw you at the armory last night, stop frontin.
When writing poetry or writing for a direct audience (small group of similar people)
When writing to a general audience (large group of different people)
When writing a business document that will be read by a member of the US government