"The use of computer software to examine large volumes of data for example the sales records of a retail business in order to extract trends and relationships that may be of use in planning the business. [...]" The Penguin Concise Dictionary of Computing, 2003
"the action of searching through DATA files looking for patterns; a form of statistical analysis, with the difference that the user may not be aware of what patterns exist." Computers and IT, 2003.
"the gathering of electronically stored information, eg about shopping patterns from loyalty cards;"
The Chambers Dictionary
"Data mining is the analysis of (often large) observational data sets to find unsuspected relationships and to summarize the data in novel ways that are both understandable and useful to the data owner."
Hand, Mannila and Smyth (2001)
"Data mining, also known as knowledge-discovery in databases (KDD), is the practice of automatically searching large stores of data for patterns. To do this, data mining uses computational techniques from statistics and pattern recognition."
Wikipedia (2005)
"Data mining is defined as the process of discovering patterns in data. The process must be automatic or (more usually) semi-automatic. The patterns discovered must be meaningful in that they lead to some advantage, usually an economic advantage. The data is invariably present in substantial quantities."
Witten and Frank (2000)