Eighth track on the fifth studio album of Taylor Swift which describes a betrayal by a close friend. The remixed version features verses from Kendrick Lamar. It received a Grammy Award nomination for Best Pop Duo/Group Performance.
The music video for the track held the 24-Hour Vevo Record with 20.1 million views before being surpassed by the video for Adele's "Hello." It won MTV Video Music Awards for Video of the Year and Best Collaboration and a Grammy Award for Best Music Video.