Phreaking
/ˈfriːkɪŋ/ · Noun · Security & Infosec · Origin: 1960
Definitions
The practice of exploiting telephone systems, the precursor to computer hacking. Captain Crunch (John Draper) discovered that a toy whistle from Cap'n Crunch cereal produced a 2600 Hz tone that gave free long-distance access. Steve Jobs and Wozniak sold blue boxes before founding Apple.
In plain English: Hacking telephone systems — the original form of hacking, done with whistles and electronics before computers were widespread.