One of the things you may come across in photography school is Conceptual Photography. Conceptual photography differs slightly from regular photography, in that it's about the concept or idea of the photo, rather than the subject itself. In some schools of thought, conceptual photography is actually considered to be a more artistic application than other forms of photography, because it tends to incorporate aspects of abstraction as well. Though some photography schools specialize solely in the subject of conceptual photography, most photography schools at least offer some courses in it.
Most conceptual photographers aim to communicate some type of message to their viewers. The most common types of these are political and social commentaries, as well as advertisements. When making a conceptual photograph, the artist will take the various elements that make up the subject of the photograph/concept, and place those elements in the picture in a way to communicate their ideas. Though some photographers may come upon their concept through experimentation, it's usually the concept/idea that precedes the photograph.
In the past, much conceptual photography was done by hand. Nowadays it's just as common to use computer programs like Photoshop to generate the effects found in conceptual photography, though many artists still do utilize organic conceptual photography techniques.
You may have studied the work of Eugène Atget in photography school. Atget was one of the first conceptual photographers. His work, "Avenue des Gobelins," often taught in photography school classes, depicts three mannequins in a shop window. One of these mannequins is actually a live person, which the audience discovers upon closer examination. From a distance, the real man appears to be the same as the mannequins, because he's wearing similar clothing and his posture is set in a similar way. Often, Atget's photograph is interpreted as an allegory of modern civilization, communicating the uniformity that fashion and clothing generates on society.
Other famous conceptual photographers you may have studied in photography school include Man Ray, whose conceptual use of the photographic technique of solarization brought him much acclaim; Herb Ritts, who use his black and white fashion photography in a classical Greek sculpture style; Andreas Gursky, whose best known for his large format architecture and landscape photographs (an interesting fact here, Gursky's "Rhein II" became the most expensive photograph ever sold on November 8, 2011 at Christie's in New York City, when it sold for 4.3 million dollars); Cindy Sherman, one of my personal favorites, whose known for her conceptual self-portraits-Sherman's work often raises questions about the role of women in society.
Photos like Man Ray's "Le Violon d'Ingres", which shows a nude woman with the f-holes of a violin on her back, and his famous solarization work, "Julie et Margaret", which turns the women in the photograph into contours (exemplifying the depersonalization of society), are both great examples of conceptual photography. Sherman's "Untitled Film Stills" is another excellent example. In these self-portraits, which are intended to look like film stills, Sherman acts out different roles of women and depicts the fantasy of popular culture.