What is hilary duff so yesterday?

Hillary Duff is an American actress, singer, and songwriter. "So Yesterday" is a song by Duff that was released in 2003 as the lead single of her second studio album, "Metamorphosis." The song was written by Duff, along with the songwriting team The Matrix. "So Yesterday" reached number 42 on the Billboard Hot 100 chart and was also a hit internationally. The song's catchy pop-rock melody and relatable lyrics about moving on from a relationship made it a popular anthem for teens at the time of its release.