An object or creature that exhibits bilateral symmetry is balanced in a single dimension. One half is a mirror image of the other half. A human body is an example of bilateral symmetry. Other examples are an open book, a pine tree and a butterfly. Most naturally occurring creatures and plants exhibit either bilateral or radial symmetry.
Radial symmetry is characterized by a structure that exhibits balance from a central point. Some examples of radial symmetry include flowers, mandalas, snowflakes, starfish, wheels and the center of a sliced orange or onion. Radially symmetric objects can be based on three, four, five, six or more axes. Snowflakes, which are based on six axes, are a well-known example of the myriad variations that can occur from a basic premise.
Three dimensionally symmetrical objects are balanced when looked at from any direction. Objects of this type are not as common as bilaterally or radially symmetrical objects. A ball, a drop of oil suspended in water and a planet are all symmetrical in three dimensions.
Temporal symmetry is exhibited by events rather than things. An example would be a musical composition that begins quietly, rises to a crescendo and then descends back to quiet at the same rate that it rose. Its symmetry is exhibited through time rather than through space. A certain level of temporal symmetry is shown in many human lives: Babies are first cared for by others, then they mature into independence and finally in old age they return to being cared for by others.