What is real ? What is illusory ? What is mind ? What is the outer world ?
Let me try to expand an answer.
Real is what it appears to be what it really is. 
Illusory is what only appears to be something, but in reality it is just a misperception of something else. 
What is the mind ? What is the outer world? … these ar tougher ones.
Let’s take the outer world. Is it real ? I am sitting on this chair. It is made of wood. I see it’s color, shape, I touch it’s surface, hear how it screeches when I sit on it. I am immersed into an abundence of sensorial input. But … how is that the picture reflected in my eye is transformed into the idea and thought of the chair in my brain ? Do we realize that our ordinary preception is based on a lot of automatic and subconscious procesess ? It is clear that we are not conscious about how our sense organs work, they just operate automatically, like complex bio-chemical mechanisms. What happens in the brain ? How a picture, what has for long ceased to be a picture and it is probably some kind of data transmitted by neurons, becomes the idea of the chair in our mind ? If we think this way, we must realize that our sense organs and even our brain still belong to the ourter world, in the sense that they are ruled by the laws of the outer world, they are built for the experience of the outer world. Than what makes a human being have a consciousness instead of being an automat ? What makes me remember myself and the outer world ? Think of this: we lose self consciousness while we are sleeping. For us, when we are sleeping, the outer world ceases to exist. The only reason we percieve it as existing is because next morning, coming back to our senses, we find it to be there again, and we recognize it to be the same. Or slightly changed, yet we are able to recognize the changes because we have the memory of the former state. Indeed, we must say, the existence of the outer world is linked to our ability to remember. If we had not this ability the world would appear every day like it appears to a newborn. But what is this ability ro remember ?
We need to realize that our clear perception of the outer world is the result of our growth process. The newborn does not see clearly, does not percieve spatiality, and even if he/she has sensorial expereinces they are meaningless/frightening, except for those what have been expereinced in the womb. (body rythms, sounds, voice fo the mother and so on)
We grow into this world, and it is quite a long process, until the child is able to speak in first person, talk using sentences, develops the ability to remember. It takes about three years.
Can we honestly say that what we call our mind has been there before this early age ?
We must admit that we have few memories before the time we were first able to say, I am. Before that, like we were sleeping. We do not even have the sense of continuity of our existence, just like while sleeping.
Now, that what we call mind and outer world are presented in this fashion, we must ask: how can we research them, not superficially, but in depth, with their links to the human being ? Do we accept the limits of our clear consciousness and self, these being our waking state and that of life between the age of three and up to our death ? If not, than we must say that perception of the outer world, and it’s mental representation are just of a relative reality.
The yogis say, if something did not exist before, and ceases to exist at a certain time, than that something has not been really existing between these two ends … but it has been an appeareance, an illusion. Meaning that it’s reality is relative. It is the result of something else, what we do not see. So, if we want to give meaning to our existence beyond it’s changing nature between birth and death, we need to accept that it is but manifestation of something we are unable to percieve. If we do not accept this, than we must accept that our very existence is unreal togheter with that of the world.
To arrive to better knowledge in this field the higher stages of meditation needs to be practiced. Pratyahara, dharana, dhyana. What makes these stages hard is that they are counterintuitive for a sensorial mind. They use and develop abilites what we rarely use in our everyday lives. In a way, the yogi needs to put himself into a state before the age of three shutting out all learnt knowledge, all subconscious conditionings, and developing the strenght of remembrence what is able to go to a “higher” level of existence, that existence of what this world we know is but a manifestation.