Wynn made a very good post about the qualities of Arahants (the early Buddhist term for enlightened individuals) at #148. The references in that post are among the most authoritative ancient sources describing what the early Buddhist community's understanding of enlightenment was. I posted my own views at #181 and #198. They were intended as little more than a simple paraphrase of some of this material. Obviously not all present-day Buddhist traditions understand these things in precisely the way that the early community did. There have been many doctrinal developments since. The Mahayana generated an elaborate Buddhology, elevated the Bodhisattva ideal, and downplayed the Arahant. Ch'an/Zen kind of merged Buddhism (mostly Mahayana's Yogacara philosophical/meditation tradition I think) with native Chinese philosophical Daoism, and arrived at new understandings of their own. I'm not a student of Zen, so I will leave the explanation of how they understand enlightenment to them. And even more obviously, the idea of 'enlightenment' isn't unique to Buddhism. It's found in other traditions as well, such as Hindu Vedanta. In fact, there's a whole variety of Vedantic understandings of enlightenment, depending on which school of Vedanta one adheres to. Again, I'll leave explanation of that to the Vedantists. Broadly speaking, the idea of 'enlightenment' is kind of indicative of the whole 'gnostic' tendency in religion, where the religious path is conceived of as learning some transformative truth. We find versions of this kind of idea all over the world, in the West as well as the East. So there probably isn't any single consensus as to what 'enlightenment' means. That's going to be a function of which tradition we are talking about, and each tradition's understanding will depend on how they conceptualize the transformative gnosis that they seek.