Symmetry
A composition in which one half of the frame mirrors the other across a vertical, horizontal or radial axis.
In depth
Symmetry conveys order, stability and formality, and it demands precision — a symmetrical composition that is a degree off looks like a mistake rather than a choice. It is most powerful when something breaks it slightly, since the eye finds the deviation immediately and that deviation becomes the subject.
Examples in practice
A cathedral nave shot exactly on axis reads as ordered, with a single figure off-centre becoming the whole point of the picture.