Back to back is defined as things that are next to each other or a situation in which one thing immediately follows another.
(adjective)An example of back to back is when you have English class and then you have math class immediately afterwards with no break.
The definition of back to back is when two things are close together or touching.
(adjective)An example of back to back is when the seats in a bus face opposite directions causing people to sit with their backs touching.