Data mining refers to the use of software that gathers information on hands played by third party players, for games in which you don't take part.
These programs observe various tables and take in thousands of hands, so that a player can later analise them and incorporate this knowledge into his game. In this way, it is possible to know something about an opponent's style of play without ever having encountered him on the tables.
Data mining is forbidden by many online platforms, as it is viewed as cheating. It is therefore subject to the same kind of regulations as pokerbots, e.g. inspection of running processes on a client's machine for suspicous activity. In general, the use of central databases pulled from the internet or available for a monthly fee, is also forbidden.