They're standing back to back.
they are standing back to back
John and Mary are standing back to back.
The father and son/daughter are standing back to back.
they are standing back to back
If you stand back-to-back. you will both be standing behind one another.
they are standing back to back A guy named John is standing in front of Peter, while peter is standing in front of another guy named John.
they are back to back
They are standing Back to back
When it is standing on its back feet, an adult male polar bear can be up to 3 metres tall.
Stand behind them on any of the 24 time zone lines, with both of you facing west. You'll be standing physically behind them, while they are standing an hour (or a day, if on the IDL) behind you.
standing up with your back straight.