Consciousness is a process (biochemical and electrical reactions between neurons) where the brain evaluates incoming (or new, self created) information against the data that has already been stored in it.
It can be other organs or cells too, not just the brain, (example - heliotropism), depends on the life form.
- What Is Consciousness? 
- Certain members have disproved the existence of consciousness, for instance Baron Max. He showed that humans are simple automatons.