Definition from the article in Wikipedeia:
Sonification is the use of non-speech audio to convey information or perceptualize data. Auditory perception has advantages in temporal, spatial, amplitude, and frequency resolution that open possibilities as an alternative or complement to visualization techniques.
Musification is the sub-specialty in which the sound is musical.
Here at IAA, we regard Sonification and Musification to be applied, or functional arts. In the same way that a graphic artist would use her artistic skills in a commercial design project, a sonification artist would use her audio and musical skills as a means to an end -- to convey or represent information.