I guess this refers to the Yin/Yang principle.
In Taoism Yang is hot, full of energy and Yin cold, lacking energy. Taoists believe that everything in the universe can be described by the Yin&Yang principle. They believe that all the forces are in constant flux, circulating between Yin and Yang.
This pictogram may seem familiar to you. It symbolizes the above mentioned circulation.
- For Teachers