Simplification
The reduction of a scene to its essential elements by choice of viewpoint, framing, focus and timing.
In depth
The eye moves constantly and edits a real scene without effort; a photograph freezes everything at equal weight, so clutter that went unnoticed in life dominates the picture. Simplification is the discipline of noticing what is in the frame rather than what you are looking at, and it is the difference between a snapshot and a photograph.
Examples in practice
Waiting until a busy square empties, or shooting against a plain wall, removes competition from the subject.