"3" is an uptempo electropop song that features a heavy bass-line and synthesizers, and lyrics that talk about threesomes, while referencing American folk-singing trio Peter, Paul and Mary during the chorus as sexual slang.
The song achieved commercial success by topping the charts in the United States and Canada, as well as reaching the top ten in many countries around the world, including Australia, Finland, Norway, Sweden and the United Kingdom.
In the United States, the song debuted at number one in the Billboard Hot 100, becoming the first to debut at the top position in over three years and the first non-American Idol artist in eleven years to do so.
"3" was also the fifteenth song in the history of Billboard to debut at number one.
An accompanying music video for "3", directed by Diane Martel, features Spears and her dancers in front of different black and white backgrounds.