Phreaking is a slang term coined to describe the activity of a culture of people who study, experiment with, or explore telecommunication systems, such as equipment and systems connected to public telephone networks. As telephone networks have become computerized, phreaking has become closely linked with computer hacking.
The term phreak is a combination of the words phone and freak, and may also refer to the use of various audio frequencies to manipulate a phone system. A large percentage of the phone Phreaks were blind.
Learn more about Phreaking on Wikipedia.