Piracy is an act of robbery or criminal violence by ship or boat-borne attackers upon another ship or a coastal area, typically with the goal of stealing cargo and other valuable goods.(1)

This term was coopted by the MAFIAA because literal descriptions such as file sharing or unauthorized copying are not objectionable to the general public who see them as minor / insignificant and thus are not sensational enough to draw the outrage needed to enact disproportionate criminal penalties(3) and thus preserve their monopolistic(2) profits.

1 - https://en.wikipedia.org/wiki/Piracy

2 - By way of ridiculously long copyright terms or distribution oligopolies / monopolies

3 - See 'conspiracy to commit' charges carrying de-facto life in prison penalties