I agree with Ken. "Ambiguity" doesn't come close to adequately describing what makes street photography street photography. And I don't even like the term "street photography." I wish there were a better name for it. If you don't know much about the history of photography the term "street photography" implies that you can grab a camera, go out in the street, start shooting, and have street photography. And that assumption seems sensible even if it's wrong.
Street photography's development goes back at least as far as Andre Kertesz, but it really was defined by Henri Cartier-Bresson. Young Henri was one of André Breton's acolytes. He'd attend Breton's gatherings and sit silently in awe during the discussions of surrealism and readings of André's surrealist poems, and when he started walking the streets of Paris with his Leica the surrealism spilled over into his photography. But those early pictures aren't quite surrealistic, and, I think, "ambiguity" comes as close as any word I can find to describe the merger of surrealism and the kind of realism you can't avoid within a well-composed photograph. When Cartier-Bresson joined with Bob Capa, Chim, George Rodger and Bill Vandivert to start Magnum, Capa had to advise him to avoid the "little surrealist" reputation being hung on him and call himself a photojournalist.
Which brings us to the difference between street photography and journalism, or, to put it in a more general way, documentation. As I'm sure Seamus with his background in journalism can tell you, for the most part photographs to be used in journalism can't afford to be surrealistic or even ambiguous. The whole point of photojournalism is explication, and surrealism most emphatically doesn't explain. But I said "for the most part." I've seen plenty of photojournalistic spreads in magazines like Life or Look where the central photograph was ambiguous enough to grab your attention and get you to read the article. Often the photojournalism was by HCB.
So if someone can come up with a better term than "street photograph" for a photograph that includes people or their artifacts in somewhat surrealistic juxtapositions, let's have it. But, as I've said before, there's no way to come to terms with the definition of whatever you call that kind of photography without studying its early masters. Words can point to it but they can't define it. You need to internalize the art to understand.