can some one clearify something about U.S. geography for me

so i was given some statistics in class on the District of Columbia, DC suburb, and Metropolitan DC, and i was just wondering whats the difference between these three areas, or are they even different areas? thanks for the help

Google. Ever heard of it?

All the same on a big map, different on a map of DC

i did try google but i cant find any site that really makes a distinction about the 3 areas