Most people have heard that the Lord Buddha was enlightened, and also know that most Buddhists practice to seek enlightenment. But what does that mean, exactly? What is enlightenment, and how do you know when you've "got" it?
"Enlightenment" is an English word that can mean several things. In western culture, the word "enlightenment" is often associated with intellect and knowledge. But Buddhist enlightenment is something else. Enlightenment in Buddhism mean to Bodhi.
Bodhi is a Sanskrit and Pali word that means "awakening," and it also is often translated as "enlightenment."
In Theravada Buddhism, bodhi is associated with the perfection of insight into the Four Noble Truths, which brings about the cessation of dukkha (suffering; stress; dissatisfaction). The person who has perfected this insight and abandoned all defilements is an arhat, one who is liberated from the cycle of samsara. While alive he enters a sort of conditional nirvana, and at death he enjoys the peace of complete nirvana.
Source : by Phra Samarth Govito