As a child I played with magic. Not this wicca magick stuff you read about online all the time - I'm referring to having my little book of magic tricks. Card tricks, things with other objects, etc. Illusions. I loved going to David Copperfield shows - even though I knew it was all illusion.
In the 12th grade we did quite a bit of Shakespeare (we'd done Shakespeare in other years, too, but not as much), and as The Tempest was one of the works studied, we dealt often with the opposition illusion and reality. Of course, we can take this all the way back to Plato and the allegory of the cave.
College, especially German courses, provided another chance to work with illusion and reality, for German Idealism was a major topic. Among other things, we had the Form/Stoff dichotomy, the Apollonian/Dionysian dichtomy, etc. -- in each case, the "formal" aspect was illusion, under which could be found the bare, naked reality.
Amazing how the term illusion requires reality as an opposite - illusion is less-real than reality not only because what it presents is merely illusion, it is a falsehood, but it is a layer on top of so-called reality.
However, illusion is not the same as being un-real. Insofar as constructs are illusions, gender is an illusion - a construct- and should be un-real, but it is obviously the case that gender has real consequences. And race, for example. Clearly a construct - and an illusion? - but it has dire consequences.
Furthermore, what if we cannot differentiate illusion and reality - what if we can never "really" get at reality, does it then make sense to speak of illusion and reality? Is it not then the case that our dichotomy between those two opposites, too, is an illusion?