back and front; inside and outside; both sides
inside out (e.g. clothing)
double-dealing; two faces (cf. two-faced)
outward appearance and actual condition; inner workings
封筒の裏表を確認した。
I checked the front and back of the envelope.
シャツの裏表を間違えていた。
I had my shirt on inside out.
紙の裏表を使って印刷すれば、節約になる。
Printing on both sides of the paper helps save resources.