What is a high street store? And where can I find.....?

I was told to go to a high street store to find something to wear for an overweight woman to sons graduation! What are some examples of a high street store? I live in Omaha, Nebraska. Also was told to try SPANX. Where can I find them besides ordering online??? Help, graduation is in 2 weeks!!! Also something not extremely expensive would be good, I'm trying to give most money to son, not on clothes, but yet wanna look good too cuz I have to walk across stage w/ him!! Don't want him (or me) to be embarrased of overweight mom!!|||"high street" is a term meaning main street or main thoroughfare of a town or city...this term is more commonly used in the u.k....