The word ain't isn't officially recognized in the dictionary. That doesn't make it uncommon, though. It is used often as a slang term that can mean "isn't it?" "it is," "is not," "am not," "are not," "have not," or "has not." That's a lot of meanings for one word, which no doubt contributes to its popularity and continued use. Similar to the word ya'll (you all), ain't is common in the southern United States.

This isn't any old vocab lesson, though. This is about Taylor Swift. Even though she hails from Pennsylvania, she picked up ain't somewhere along the way and has used it in her songs. She has continued to use the word since her transition from country to pop music.