Rosa Parks is a black civil rights activist from Alabama famous for refusing to give up her seat on a bus. In 1955, while riding the bus home from work, the driver ordered her to move to the back of the bus so a white man could have her seat. She refused and was arrested. This led to outrage in the black community, who boycotted public transportation in the city of Montgomery. It was a turning point in the US civil rights movement, as after a year of boycotts, segregation on busses was ruled unconstitutional. During the boycotts, Martin Luther King Jr. emerged as a leader in the black community, and was praised for his tactics of peaceful civil disobedience.
The song is about the entertainment industry. Parks is not actually mentioned in the lyrics and has nothing to do with the song, but she is referred to in the chorus of "Move to the back of the bus."
Parks sued Outkast over this, claiming it exploited her image. The case was settled in 2005, with Outkast and their record company agreeing "To enlighten today's youth about the significant role Rosa Parks played in making America a better place for all races." Parks was 92 when the case was settled.
The harmonica solo is by Pastor Robert Hodo, the stepfather of Outkast's Andre 3000.
This plays in the ESPN 10-part documentary The Last Dance in a scene where Michael Jordan's Chicago Bulls play the Atlanta Hawks in 1998. The song is appropriate to the era, and Outkast is from Atlanta, giving it a strong connection to the scene.