The verbal meaning of Adharma is irreligiosity. Blind faith, that which disregards the cosmic principles leads to adharma. Adharmas are those actions which are contrary to the individuals dharma.
Anything which is working contrary to the laws of existence is adharma. For example, at sunrise the whole existence changes, becomes vibrant, the atmospheric pressures and temperatures change. The tempo of life increases. Sleeping at this time is acting contrary to the laws of the planet, thus it is adharma.
Looting the Mother Earth for natural resources, which are then employed without concern for their negative effects on the environment and the future needs of the planet, is adharma against the earth. Similarily, there are adharmas related to one's own physiology. Denying one's own self is adharma. Self-rejection and self-praise are both adharmas. Self-destruction is the greatest adharma.
Adharma is best understood as an imbalance in the three gunas, the three primary cosmic forces responsible for all manifestations. When either sattva (conscious energy), tamas (inertia), or rajas (motion) are more dominant than the situation allows, adharma takes birth.
These imbalances or adharmas can be controlled by faith, devotion, or bhakti, which is the essence of the fourth chakra. Faith can lead the yogi - if he acts in harmony with his true nature, sudharma - to the plane of austerity. But if it is not in tune with his innermost vibrations, it can draw him back to delusion. So the faith should not be blind faith. Faith alone, without grounding in the laws of existence, is blind faith. And blind faith is the most frequent cause of energy loss in this plane of being. If faith is in tune with the law of existence it is called sudharma.