When two dj's 'b2b' what does this mean

"B2B", in the context of DJing, refers to working together "back to back". B2B is when two DJs spin music together, taking turns with each playing usually two to three tracks.

Some DJ duos prefer to do about 5 tunes apiece before swapping. As time goes on with two DJs doing B2B work, they tend to become familiar with each others' styles and working off each others' mixes really well. Often such relationships evolve into long-term working relationships doing B2B work.