The A.V. Club (short for Audio-Visual Club) is a club at McKinley. They are sometimes in charge of making different props or decorations for occasions in the school, like the ones in Season Two. Unlike most other clubs, Rachel is not a member of this one.
Rachel approaches Lauren who is the president of The A.V. Club. She has her set up various microphones in the Choir Room to help catch those who are not singing. And later on, Rachel finds out that Finn, Quinn, Santana, Puck and Brittany are the members who are not singing and shows the list to Mr. Schue .
Rachel brings Finn to the auditorium to sing Merry Christmas Darling for him. The A.V. Club has presumably set up a winter wonderland on the stage, and even rigged snow machines to enhance Rachel's performance.
The members are making decorations for the prom in the auditorium when Rachel asks them to tell her their opinion on the song she was going to sing. The members then sing backup in Rolling in the Deep.