What is Enlightment
Enlightenment is seeing self-nature. Some called this nature "buddha-nature" or the "nature of emptiness." When one has no attachment to the notion of "self," one's attitude in dealing with any situation is called wisdom.
Wisdom is basically a selfless attitude. When wisdom manifests, one's nature is seen. The notion of "self" here can refer to an individual self, a group of selves, or the universe as an all-encompassing self.
When you practice, you might encounter all kinds of physical and mental experiences. For example, you may feel like you are in the state of unity; you feel like you have completely unified with the universe. These phenomena may enhance your confidence and faith in your practice and in the Dharma. This is not, however, genuine enlightenment.
Genuine enlightenment must be in accord with the principles described by the sixth patriarch, Master Huineng: no-form, no-thought, and no-abiding. When the mind functions without abiding, it is called "no thought". No form means no unchanging or definite form. Wherever there are phenomena, there is illusion.