In the context of my research, rendering refers to the digital representation of an objects surface using computer software such as Mental Ray or Keyshot.
This software calculates how the available light and environment both illuminate and reflect off the surface, based upon orientation to the camera, light and materials surface properties.
This representation, when coupled with Image Based Lighting techniques is considered ‘photo-realistic’
When solely using a HDR image, that representation can be considered 100% (or as near as to the ‘real world’ scenario)
Introduction of supplementary light sources (or manipulation of the HDR) can be considered ‘artistic representations’ of the scenario.