The country singer, who has in the past dated Joe Jonas and Taylor Lautner, told MTV News that the tune is about when a relationship comes to an end.
She said: 'I was at an awards show, and there was a guy there, obviously - it all starts there, doesn't it?
'It was a guy I had been in a relationship with, falling out, then we ended up at the same awards show.'
Swift added: 'Both trying to act like we don't care... both like, chatting up the people next to us.'
After that happened Taylor decided to write a song about the experience.
She added: 'Afterward, I just felt so empty, like we were both fighting this silent war of pretending we didn't care that the other was there.
'And I went home, and I wrote this song about it and at that point, I had this gut feeling, and I knew the album was finished.'