when back is turned
when somebody's back is turnedalso while somebody's back is turned
when someone is not watching what is happening When my mother's back was turned, my grandmother would give the dog candy.
when/while somebody's back is turned
while someone is somewhere else or unable to notice what is happening When my mother's back was turned, my grandmother would give me chocolates.See be [glad etc.] to see the back of, break back, know like the back of hand, ride on the back of, stab in the back, talk out of the back of head, turn back on, watch back, You scratch my back and I'll scratch yours, break the back of, cover back, be back on the rails