noun

• (twenty-one) the natural number following 20 and preceding 22.
• 21, Bagram, or Twenty Plus One is a drinking game.
• the second studio album by American R&B singer Omarion.
• "21" is the debut single by The Paddingtons, released on 11 October 2004, which was later re-recorded for the album First Comes First.
• a 2008 American heist drama film directed by Robert Luketic and starring Jim Sturgess, Kevin Spacey, Laurence Fishburne, Kate Bosworth, Liza Lapira, Jacob Pitts, Aaron Yoo, and Kieu Chinh.
• the second studio album by English singer-songwriter Adele.
• the 21st studio album by German heavy metal band Rage, released on 24 February 2012 through Nuclear Blast Records.
• "21" is the first episode of the second season of the HBO television series Boardwalk Empire, which originally aired September 25, 2011.
• "21" is a song recorded by American country music singer Hunter Hayes as the lead single for his third studio album The 21 Project.
• the second extended play by American country music artist Hunter Hayes, released to streaming services on August 7, 2015.
• "21" is a song by American rapper Polo G from his second studio album The Goat.