Many definitions of sonification have been proposed. The one I like the best was written by Carla Scaletti:

“A mapping of numerically represented relations in some domain under study to relations in an acoustic domain for the purposes of interpreting, understanding, or communicating relations in the domain under study.”

Carla puts it even more simply on her website: “The process of mapping data to sound in order to better understand the data.”

On her website, Carla also makes the following statement with which I completely agree: “Sonification is not music.  But music is a sonification.” In her fascinating Keynote Address "Music is Not a Language" at the Kyma International Sound Symposium, Sept. 2010, Carla suggests a direct connection between music and thought, in which language is not involved.

If music is a sonification of the thought process of the composer, then it is intriguing to speculate what form of meaning could be conveyed via the sonification of complex data. The sounds could convey meaning, directly, out of reach and beyond the realm of language.