Kant's Definition of Enlightenment
In his famous 1784 essay "What Is Enlightenment", Immanuel Kant defined it as follows:
"Enlightenment is man's emergence from his self-incurred immaturity. Immaturity is the inability to use one's own understanding without the guidance of another. This immaturity is self-incurred if its cause is not lack of understanding, but lack of resolution and courage to use it without the guidance of another. The motto of enlightenment is therefore: Sapere aude! Have courage to use your own understanding!"
Spirituality and Enlightenment
Enlightenment, as a concept related to the Buddhist Bodhi, and equally, the Christian and Judaic idea of spiritual knowledge, is a cornerstone of modern religious and spiritual understanding. The term "enlightenment" is often used as a secular idea that relates to a localized, religion-specific "enlightenment", and also attempts to bridge the traditional gap between religions and religious belief and psychological science.
The "age of enlightenment" is a proverbial reference to a time of maturing in people -- roughly around the age of 18 years -- when the illusions of childhood lift, and one is left with greater self-awareness and understanding of their own roles and responsibilities in the world. This is analogous to the Christian-adopted concept of being "born-again" and is a direct tie between the spiritual teachings of The Christ, Jesus and The Buddha.