言外之意 The meaning outside the words. A meaning that is implied but not stated clearly.
弦外之音 The sound beyond the strings. Originally the lingering sound of music. Today a meaning that comes through indirectly in what is said.
心照不宣 Hearts reflect each other, nothing is declared. Both sides understand, and there is no need to say it.
拐弯抹角 To turn bends and go around corners. To speak without coming straight to the point.