"Real," in my experience, is supposed to describe that which is totally independent, or at least may be interpreted as existing independently. It's that idea of atomics, of base units or smallest, indivisible parts, that gives rise to this definition of reality; we look for the lines around things so that we can understand them, but to do this we must first believe in separateness. Our ideas must be made bite-sized for us to digest them.
This line of reasoning, I think, is what ever inspired someone to imagine themselves the only person who "really" existed, all else being but synapse or dream. Pretentious as I've found this idea since my third second considering it, I must say I agree with the argument; it is terminology that fails us. "Real" is only useful as a concept, like any other, if it identifies a contrast; if everything were "real," or just as much if nothing were, the idea couldn't exist just because it could never come up in conversation. So the question becomes: is anything totally independent?
Back to that staple of existentialism, "I am the only person who really exists, everyone else is just in my head." Where does this notion come from? If I experience another person and am in any way surprised by anything they ever do, isn't the debate settled? How could I surprise myself, after all, or learn anything new if everything is already in my mind? Much in the same way I might learn new words while knowing the English alphabet by heart, or new ideas while being fluent in the English language: I apply an existing method for interpreting my experiences to the new and varied events that come to me.
Come, but from where? This is where my faith in a world outside my mind comes from: the novelty of life experience. This can only ever be faith, however, because that world, whatever it's like, is so abstract and removed from myself that it may as well not exist. My experiences, after all, aren't of these "real" things, but my interpretations of them. Interpretations, loaded with my preferences and preconceptions, dependent on my patience and curiosity, in any practical sense are just in my head. I don't see you; I look at you, but see only the bit of which I am capable, and even then only admit to seeing the tiny sliver I wish to see; much as if I interpreted a brown crayon as the letter 'b' because, well, there is a 'b' there.
In this way, being that I must actively participate in anything I experience of the outside world, none of it would qualify as "real" in the sense of being independent. Am I all that's left, then? The only truly independent mind in existence, woe is me...
No, I am as much a conversation between these elusive "real" things as anyone else: Earth and Sun converse in the language of life, body and mind in that of biology, and each is itself the meeting point of various other physical and psychological factors. I am here, completely and totally, because other things were here before me which could and did bring about my existence. My day-to-day life is as it is because of a conversation between myself and the world around me: I say what I want, you do the same, and if we're lucky we find some common ground before we kill each other with miscommunication.
