Senses
背对背/ 背對背 back to back
with backs toward each other; with one's back turned to another person
背对背/ 背對背 behind one's back
doing something without the involvement or presence of the parties concerned; privately; also written 背靠背
with backs toward each other; with one's back turned to another person
doing something without the involvement or presence of the parties concerned; privately; also written 背靠背