Enlightenment in the Eastern sense means realising your true self, or becoming totally aware and conscious, and living in the present moment. It is a permanent state, as distinct from glimpses of enlightenment, which are referred to as satoris.
Osho describes it thus: ‘Enlightenment simply means an experience of your consciousness unclouded by past emotions, sentiments … When the consciousness is totally empty, there is something like an explosion – like an atomic explosion … Your whole inside becomes full of light which has no source and no cause or past, and once it has happened it remains. It never leaves you for a single moment. Even when you are asleep that light is inside, and after that moment you can see things in a totally different way.’
See Osho’s full description of his enlightenment here.