Focal Point
The element in a photograph that the eye is drawn to first and returns to.
In depth
The eye is attracted by sharpness, contrast, brightness, saturation, faces and convergence — so a focal point is created by making one area win on several of those at once. A photograph with two competing focal points reads as unresolved, which is why the most common fix is to weaken one rather than strengthen the other.
Examples in practice
A brightly lit face against a dark, softly rendered interior becomes the focal point without any compositional device at all.