back to back

WordReference Random House Learner's Dictionary of American English © 2025

ˈback to ˈback or ˈback-to-ˈback,adj. 

1. [usually: before a noun] following one immediately after the other;
   consecutive:
   back-to-back defeats.

WordReference Random House Unabridged Dictionary of American English © 2025

back′ to back′, 

1. adjacent or contiguous but oppositely oriented;
   having the backs close together or adjoining:
   The seats in the day coach are back to back.
2. (of two similar events) following one immediately after the other;
   in unbroken sequence;
   consecutively:
   After losing all day, he picked winners back to back in the last two races.
3. Games [Stud Poker.] having a pair, consisting of the hole card and the first upcard:
   He had aces back to back.
back′-to-back′, adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

back-to-back adjective (usually postpositive)

1. facing in opposite directions, often with the backs touching
2. (of urban houses) built so that their backs are joined or separated only by a narrow alley