Yang is one half of the primal forces that form the core of Chinese metaphysics (the other being Yin). These two energies, or forces, are believed to be present in all things; combined, yin and yang make up the energy, or Chi, of the universe.
Yang energy is dynamic in nature; it is associated with aspects such as heat, motion, strength, light and hardness. Yang is also considered a masculine energy, though both genders have Yin and Yang energy in them.
It is worth noting that though Yin and Yang represent dark and light respectively, these energies have no connection to good or evil (as is common in some Western ideas); both are considered important energies in order to maintain universal balance.
The Pillar of Mercy in the Tree of Life.