One big dirty word you should borrow from literature is "Theme." A theme is a humanely relevant issue with which you engage by formulating it in a particular way. Part of the meaning of a work of art derives from the very specific way in which one does so.
Case in point: Guernica. It's about military ruthlessness, more specifically about Franco's trial of German planes on a small innocent village. Yet it's not just a painting that's "about" war, or violence. It does so in a very specific manner. It applies form over content, if you will, and what it expresses is not a general idea, but a particularly formed one. One that exists only in that very incarnation. It also happens that this idea is powerful, moving, shocking, denunciating, and graphically stunning.
There's been too much Stieglitz and not enough Picasso in photography, if you want my opinion.