Proportion
Formal: The relative size of parts of a whole. (Sophia.org)
Informal: Parts of a whole piece.
Rule Of Thirds
Formal: aligning a subject with the guide lines and their intersection points, placing the horizon on the top or bottom line, or allowing linear features in the image to flow from section to section. (Wiki)
Informal: A precise proportion
Golden Rule
Formal: a line is divided into two parts and the longer part (a) divided by the smaller part (b) is equal to the sum of (a) + (b) divided by (a), which both equal 1.618.
Informal: Sections of a image that makes it stand out.