Pirate decryption
Note that if a band starts singing "This is Radio Clash from pirate satellite, orbiting your living room, cashing in the bill of rights..." they're most likely referring to a quite different concept, that of pirate radio which involved the operation of a small broadcast radio station without lawfully obtaining a licence to transmit.
Pirate decryption most often refers to the reception of compromised Pay TV or pay radio signals without authorisation from the original broadcaster. The term "pirate" in this case is used in the sense of copyright infringement and has little or nothing to do with clandestine transmitting stations or with sea piracy.
History
The concept of pay TV is almost as old as TV itself and involves a broadcaster deliberately transmitting signals in a non-standard, scrambled or encrypted format in order to charge viewers a sizeable subscription fee for the use of a special decoder needed to receive the scrambled broadcast signal.
Early Pay TV broadcasts in countries such as the United States used standard over-the-air transmitters; many restrictions applied as anti-siphoning laws were enacted to prevent broadcasters of scrambled signals from engaging in activities to harm the development of standard free to air commercial broadcasting. Scrambled signals were limited to large communities which already had a certain minimum number of unencrypted broadcast stations, relegated to certain frequencies only with restrictions were placed on access of pay TV broadcasters to content such as recent feature films in order to give free TV broadcasters a chance to air these programmes before they were siphoned away by pay channels.
Under these conditions, the pay TV concept was very slow to become commercially viable; most television and radio broadcasts remained in-the-clear and were funded by commercial advertising, individual and corporate donations to educational broadcasters, direct funding by governments or (in the UK) license fees charged to the owners of receiving apparatus.
Pay TV only began to become common after the widespread installation of cable television systems in the 1970's and 1980's; early premium channels were most often movie broadcasters such as the US-based Home Box Office and Cinemax, both currently owned by Time Warner. Signals were obtained for distribution by cable companies using C-band satellite dish antennas of up to ten feet in diameter; the original satellite signal was originally unencrypted as very few individual end-users could afford the large and expensive satellite receiving apparatus.
As satellite dishes became smaller and more affordable, most satellite signal providers adopted various forms of encryption in order to limit reception to certain groups (such as hôtels, or cable companies, or paid subscribers) or to specific political regions. Some free to air satellite content remains, but many of the channels still in the clear are ethnic channels, local over-the-air TV stations, religious programming, backfeeds of network programming destined to local TV stations or signals uplinked from mobile satellite trucks to provide live news and sports coverage.
Specialty channels and premium movie channels are most often encrypted; broadcasts consisting of explicit pornography must always be encrypted to prevent reception by those who choose not to see this so-called adult content.