2. The theft of ones personal property for reselling to profit.
Originating from early sailors called pirates who plundered other vessels for their goods. Todays, pirates are known also as downloaders and/or hackers (as the news media would have the general public think). Frowned upon by society, piracy has become rampant in scale via the internet and has forced authorities to arrest and prosecute the very same thing people have been doing with printing press, vcr and tape recorder since the 1920s.
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.
Nowadays, it's a synonym for 'copyright infringement', which is not the same thing as theft. Copying in moderation may well benefit the industries in many circumstances as it increases public awareness of the industries and individual products; it's the mass copying initiatives, and the counterfeit sales, that are most likely eroding sales.
In cracking down on 'piracy' the copyright police are using a sledgehammer to crack a nut, and in pissing off loyal customers with intrusive 'copy protection systems', the concept of copyright law and the relevant industries are giving themselves a bad name.
Okay, so piracy is wrong because it's against the law, and it's against the law because it's wrong. That argument doesn't work.