A gable's the generally triangular portion of a wall between the edges of a sloping roof. The shape of the gable and how it's detailed depends on the structural system being used (which's often related to climate and availability of materials) and aesthetic concerns. Thus the type of roof enclosing the volume dictates the shape of the gable. In Classic Greek and Roman architecture, the analogous feature's called the tympanum. Strictly speaking, the tympanum's the infill area, often triangular,… (More on Gable)