Generally, data mining (sometimes called data or knowledge
discovery) is the process of analyzing data from different
perspectives and summarizing it into useful information -
information that can be used to increase revenue, cuts
costs, or both. Data mining software is one of a number of
analytical tools for analyzing data. It allows users to
analyze data from many different dimensions or angles,
categorize it, and summarize the relationships identified.
Technically, data mining is the process of finding
correlations or patterns among dozens of fields in large
relational databases.

Data mining is the process of discovering hidden patterns
from the data warehouse,which users doesn't even know or
thought of asking about it.