(noun) - Proportion is a principle of art that describes the size, location or amount of one element to another (or to the whole) in a work. It has a great deal to do with the overall hamrony of an individual piece.
Think of Leonardo's Vitruvian Man (you know the guy: naked, inserted within a rectangle within a circle, arms outstretched, legs shown both together and spread, etc.) for a clear idea of just how much thought has gone into proper proportioning over the ages.

