Meaning of “back-to-back” - Learner’s Dictionary

back-to-back

adjective, adverb uk us /ˌbæktəˈbæk/
POSITION

If two people or things are back-to-back, their backs are touching or facing each other:

They stood back-to-back.
AFTER

If two things happen back-to-back, one happens after the other without a pause:

back-to-back interviews

(Definition of “back-to-back” from the Cambridge Learner’s Dictionary © Cambridge University Press)