"Reality," the concept, is contrasted with a wide variety of other concepts, largely depending upon the intellectual discipline. It can help us to understand what we mean by "reality" to note that what we say is not real because we see it through different perspectives, therefore there is no basis for reality. But usually if there is no original and related proofs, it isn't reality.
In philosophy, reality is contrasted with nonexistence (penguins do exist; so they are real) and mere possibility (a mountain made of gold is merely possible, but is not known to be real—that is, actual rather than possible—unless one is discovered). Sometimes philosophers speak as though reality is contrasted with existence itself, though ordinary language and many other philosophers would treat these as synonyms. They have in mind the notion that there is a kind of reality — a mental or intentional reality, perhaps — that imaginary objects, such as the aforementioned golden mountain, have. Alexius Meinong is famous, or infamous, for holding that such things have so-called subsistence, and thus a kind of reality, even while they do not actually exist. Most philosophers find the very notion of "subsistence" mysterious and unnecessary, and one of the shibboleths and starting points of 20th century analytic philosophy has been the forceful rejection of the notion of subsistence — of "real" but nonexistent objects.
Some schools of Buddhism hold that reality is something void of description, the formless which forms all illusions or maya. Buddhists hold that we can only discuss objects which are not reality itself and that nothing can be said of reality which is true in any absolute sense. Discussions of a permanent self are necessarily about the reality of self which cannot be pointed to nor described in any way. Similar is the Taoist saying, that the Tao that can be named is not the true Tao, or way.
It is worth saying at this point that many philosophers are not content with saying merely what reality is not — some of them have positive theories of what broad categories of objects are real, in addition. See ontology as well as philosophical realism; these topics are also briefly treated below.
In ethics, political theory, and the arts, reality is often contrasted with what is "ideal."
One of the fundamental issues in ethics is called the is-ought problem, and it can be formulated as follows: "Given our knowledge of the way the world 'is,' how can we know the way the world 'ought to be'?" Most ethical views hold that the world we live in (the real world) is not ideal — and, as such, there is room for improvement.
In the arts there was a broad movement beginning in the 19th century, realism (which led to naturalism), which sought to portray characters, scenes, and so forth, realistically. This was in contrast and reaction to romanticism, which portrayed their subjects idealistically. Commentary about these artistic movements is sometimes put in terms of the contrast between the real and the ideal: on the one hand, the average, ordinary, and natural, and on the other, the superlative, extraordinary, improbable, and sometimes even supernatural. Obviously, when speaking in this sense, "real" (or "realistic") does not have the same meaning as it does when, for example, a philosopher uses the term to distinguish, simply, what exists from what does not exist.
In the arts, and also in ordinary life, the notion of reality (or realism) is also often contrasted with illusion. A painting that precisely indicates the visually-appearing shape of a depicted object is said to be realistic in that respect; one that distorts features, as Pablo Picasso's paintings are famous for doing, are said to be unrealistic, and thus some observers will say that they are "not real." But there are also tendencies in the visual arts toward so-called realism and more recently photorealism that invite a different sort of contrast with the real. Trompe-l'œil (French, "fool the eye") paintings render their subjects so "realistically" that the casual observer might temporarily be deceived into thinking that he is seeing something, indeed, real — but in fact, it is merely an illusion, and an intentional one at that.
In psychiatry, reality, or rather the idea of being in touch with reality, is integral to the notion of schizophrenia, which has often been defined in part by reference to being "out of touch" with reality. The schizophrenic is said to have hallucinations and delusions which concern people and events that are not "real." However, there is controversy over what is considered "out of touch with reality," particularly due to the noticeable comparison of the process of forcibly institutionalising individuals for expressing their beliefs in society to reality enforcement. The practice's possible covert use as a political tool can perhaps be illustrated by the 18th century psychiatric sentences in the U.S. of black slaves for 'crazily' attempting to escape. See also anti-psychiatry and one of its prominent figures, the psychiatrist Thomas Szasz.
In each of these cases, discussions of reality, or what counts as "real," take on quite different casts; indeed, what we say about reality often depends on what we say it is not.
I am The Perception of, Reality, and Truth