Sonification is still a young research field and many terms such as sonification, auditory display, auralization, audification have been used without a precise definition. Recent developments such as the introduction of Model-based Sonification, the establishing of interactive sonification and the increased interest in sonification from arts have raised the issue of revisiting the definitions towards a clearer terminology. This paper introduces a new definition for sonification and auditory display that emphasize necessary and sufficient conditions for organized sound to be called sonification. It furthermore suggests a taxonomy, and discusses the relation between visualization and sonification. A hierarchy of closed-loop interactions is furthermore introduced. This paper aims at initiating vivid discussions towards the establishing of a deeper theory of sonification and auditory display.