The Barden Bellas are the main heroines from the Pitch Perfect movies. They are based on the Divisi and the Hullaballoos from the original book.
They are a group of young girls united due to the status as misfits in their local school, who deciced to come together as an acapella band, singing acapella covers of song. Over the course of the three movies, they graduate from college, but they stick together no matter what. They are shown to be not very bright, but have plenty of kindness, loyalty and honesty, as well as "street smarts".
The informal leader of the Bellas is the shy and meek Chloe Beale, who nevertheless has a very powerful singing voice. Aubrey Posen thinks she's the leader, but her villanous tendencies mean the other Bellas don't see her in high regard. The second in command of the Bellas is Beca Mitchell, who is sarcastic and acerbic, but still has plenty of respect and love for her fellow Bellas. The last to join was Fat Amy (who's actually named Patricia and not Amy), the quirkiest and most excentric of the team.