Thank you for asking me.
This "illusion or dream" is the "emptiness" that the Buddha revealed. "Emptiness" concept in Buddhism is a unique revelation by the Buddha. It is the 3rd characteristic of what we call the 3 characteristics of the nature of this world. The Buddha expounded the trilogy of Anicca, Dukkha, Anatta, meaning Impermanance, Unsatisfactoriness, No soul or insubstantiality or emptiness.
This concept of emptiness can only be understood if one understands the concept of Anatta. It takes some time and a lot of contemplation to understand Anatta. The underlying concept of Anatta is that in the final analysis, there is nothing in this world which we can call our own. As such it is "empty". The Pali term is called Sunnata (pronounce: Soon - ya - ta). If one can really accept this concept then one is free from the clutches of the miseries of this world.
What we are experiencing in life IS real; not exactly "emptiness" or "illusion". It is the whole futile process of living (existence) that is "emptiness" or "illusion". Now let us be an observer of a life cycle of a butterfly. First the egg, then the caterpillar, followed by the pupa in the chrysalis, and finally emerged the butterfly. All this process took only a few weeks, and the butterfly will die after another two weeks. As an observer, we can SEE the futility of this cycle which is real; but don't we see the "emptiness" in this process? As far as the butterfly is concerned, it is a real life. As far as we observers are concerned, it is just a passing passage of one very short life. This to me relates very well to the concept of "emptiness". Imagine the butterfly to be you, maybe you could see this "emptiness" for real!
I would suggest you study the basic concepts of Buddhism first before going into the deeper discussion of Buddhist concepts. Also bear in mind there are slight differences in Buddhist interpretations by the different traditions. The "mother" of all Buddhist web sites is www.budhanet.net which you will be given all the relevent links to all Buddhist subjects.
Hope this helps.