I always heard it called the "neutral" accent. Try telling that to someone from the UK.
Interestingly, everyone in the US can understand nearly everyone else. A Californian can understand Bernie Sanders, and someone from Maine can understand Tulsi Gabbard.
On the other hand, casual Spanish from Mexico is hard to understand in Argentina or Puerto Rico, both due to accent and word usage and meaning. The most extreme case I have seen is a Mexico City "street" movie which had Spanish subtitles for the rest of Mexico.
Sometimes we don't realize how "united" the United States really are.