Enlightenment

The English term enlightenment has been used to translate several Buddhist terms and concepts, most notably bodhi, kensho and satori

Kensho and Satori are Japanese terms used in Zen traditions. Kensho means "seeing into one's true nature." Ken means "seeing", sho means "nature", "essence
Bodhi literally means "to have woken up and understood" and refers to the particular form of understanding or knowledge that the Buddha attained upon his awakening. This knowledge is an understanding into the causality by which sentient beings come into existence, as well as the operations of the mind which keep sentient beings imprisoned in craving, suffering and rebirth. Bodhi is thus the understanding of the way to liberate oneself from this imprisonment.

In this awakening it is realized that observer and observed are not distinct entities, but mutual co-dependent.

In the Vanapattha Sutta  the Buddha describes  the jungle of life, and the attainment of awakening. After destroying the disturbances of the mind, and attaining concentration of the mind a meditative state , he attained three knowledge's 

1. Insight in his past lives
2. Insight in the workings of Karma and Reincarnation
3. Insight in the Four Noble Truths

Insight in the Four Noble Truths is here being called awakening

The four noble truths are:

1. The truth of dukkha (suffering, anxiety, dissatisfaction)
2. The truth of the origin of dukkha
3. The truth of the cessation of dukkha
4. The truth of the path leading to the cessation of dukkha

Awakening or enlightenment  is also being described as reaching Nirvana, the extinction of the passions whereby suffering is ended and no more rebirths take place.The insight arises that this liberation is certain:

Knowledge arose in me, and insight: my freedom is certain, this is my last birth, now there is no rebirth