B-stage
A B-stage is a small, secondary stage, featured at pop and rock concerts held in arenas and stadiums, and is usually located in the middle of the concert floor, connected to the main stage by a catwalk.
Origins
The B-stage was originally used in the early 1990s by U2 on their Zoo TV Tour. It provided a more intimate setting for stripped-down, quieter versions of songs, that could be played in greater proximity to the audience.
Current examples
B-stages are still commonly used, having become a standard feature of large rock and pop concerts.
Madonna
Madonna has used a B-stage in four of her nine tours starting with Girlie Show, Confessions tour, Sticky and Sweet tour and Mdna tour, connected by a catwalk. In Mdna she has employed a "V" catwalk to connect the main stage with the B stage.
Aerosmith and Bon Jovi
Aerosmith has employed a B-stage on almost every tour since 2001 (sometimes connected by a catwalk). During their outdoor amphitheater performances from 2001–2003, Aerosmith would play three songs on this stage during the middle of the show, and in more recent years, the band members go back and forth between the main stage and the B-stage throughout their performances via a catwalk. Bon Jovi made use of such a stage during their 2008 Lost Highway Tour in which Jon Bon Jovi (and sometimes Richie Sambora) would sing ballads such as "Bed of Roses", "Always", or "Living in Sin" from a smaller stage closer to the crowd, while the rest of the band performed on the main stage.