Old usage: the act of sailing around on a huge boat with a bunch of other guys (all of whom most likely are missing either one of their legs, hands, or eyes) and raiding spanish galleons up and down whatever coast you happen to be on. This action usually involves a lot of town pillaging, treasure looting, booty stealing, cutlass weilding, ARRR! yelling, parrot having, musket shooting, rum drinking, accordion playing, cannon cannoning, and buggery.
New usage: the act of stealing music, movies, unlicensed software, etc off of the internet. Usually done through a variety of p2p
clients. This practice is of course denounced by the industry and they have launched a campaign of legal action and anti-piracy media featuring the likes of M E Hart
aimed at destroying piracy, but all indications as of now are that it will survive.
In both cases, piracy is awesome.