Yin and Yang
Yin and yang are two opposing elements of the universe, however they are not two definite concepts, like good and evil; instead they are relative.
Yin: association with the dark moon (facing away from Sun), represents feminine nature
Yang: association with the bright sun, represents masculine nature
Yin and yang can also be used (in conjunction with other characters) to indicate various behaviours.
A modern example:
Yin: traffic obeying a traffic light (stillness)
Yang: traffic going through a red traffic light (the vivaciousness)
Some Chinese, Korean and Japanese place names that still exist are named in the following principle:
Yin: the north side of the mountain, the south side of the river.
Yang: the south side of the mountain, the north side of the river.