oxymoron
The phrase "awfully good" is contradictory. Something that is awful is usually considered bad, but in this case the adverb describes the adjective good. It means that his mother's cheesecake is very good, not awful. An oxymoron is a phrase of opposites, usually just two words. Some other examples of oxymorons are "jumbo shrimp", "dry ice", and "icy hot". There are all phrases with words that contradict each other.
