Concept: Let's see the most common definition.

Is this: "An information extraction activity whose goal is to discover hidden facts contained in data bases".

In most cases the activity refers to an automated job. If any human is in the middle of the process, it's not considered as Data Mining by many people.

The word "discover" is related to the fact that the most valuable information is not previously known; however, these techniques may help to confirm any suspected behavior of the system in a particular context.

Regarding hidden facts, they will be mainly under the forms of rules; which help us to understand the model of the system related to the observed data. On the other hand, those rules may be used in the prediction of certain states.

Some times, the task may be seen in a simpler way as a mechanism to classify events.