Iconography refers to symbolism used in an image. For example, in this sculpture (which originally had a head and arms),we see the Roman winged, known in ancient Greece as Nike. It is important to determine the time period in which this was created. Had this work of art been sculpted during the Christian era, one might assume it was an angel, or a winged representation. The subject matter of an artwork merely refers to what you see; a description of the image.