What is the meaning of Back-to-back?

Sequential or consecutive.

With one's back facing that of somebody else.

Emerging in exactly opposite directions.

Having a party wall at the rear,

Synonym of wired (being a pair in seven card stud with one face up and one face down).

Alternative form of back to back

A house with a party wall at the rear.

One of a pair of rig workers who are rostered on alternately.

Source: wiktionary.org