What is Data Mining?
Gregory Piatetsky-Shapiro answers:
Data Mining is the process of finding new and potentially useful knowledge from data.
A simpler definition is:
Data Mining is the art and science of finding interesting and useful patterns in data.
See a basic introductory article "From Data Mining to Knowledge Discovery in Databases", U. Fayyad, G. Piatetsky-Shapiro, and P. Smyth, AI Magazine 1996.
See also KDnuggets publications page