What is datamining?

I ran a search on this, but I couldn't find a post to explain it so...
Can someone explain datamining to me? Do you have to be seated at the table to do it? It is illegal/unethical? I have PokerTracker but usually not enough hands in it to get good reads. Thanks.

[Tk79]

Datamining is importing observed hands. All you have to do is have the table open and have poker tracker importing. On the party auto import window click on observed hands and make sure that "Do not import observed hand history files at this time" is not checked.