Intellectual property is a catch-all term for a number of legal concepts, including trademarks, commercial secrets, patents, and copyright.
The term has its uses among the legal profession - it can be considered a category of law.
However, it is increasingly being used in a manner that creates the false analogy between property and ideas. The reason it has become widespread is that 'intellectual property' owners1 wish to exert an increasing level of control over their 'property', under the (possibly misguided) perception that digital dissemination of data forces issues such as ownership to extremities.
The definitions below refer to the US legal system.
A trademark is an identifier for a company or product that is afforded legal protection. This helps competition by providing brand-distinction and preventing the corporate equivalent of identity theft. Parody of trademarks is legally protected.
A commercial secret also known as a trade secret is to a company what documents marked classified and above are to a government. Before being given access to a trade secret, you will probably be asked to sign an NDA. No part of a trade secret may be released without breaking either a law or a contract. Misappropriation of trade secrets is punishable under the Economic Espionage Act of 1996.
A patent is granted on an invention, and grants exclusivity on benefits derived from that invention. This exclusivity is granted as an incentive to invent. An example of an invention would be the Segway. However, the term 'invention' now includes algorithms and business processes. Examples of these include RSA and One-click shopping.
A copyright in the traditional sense is a time-limited monopoly on distribution of a creative work. This is intended to make sure that the author of a creative work benefits. Copyright was introduced shortly after the printing press was invented, and large-scale copyright infringement (aka piracy2) became possible.3 Recently, the Sonny Bono Copyright Extension Act allows corporate-owned copyright to be renewed more or less indefinitely. Mickey Mouse is the prime example and the motivation behind Michael Eisner's backing of the act.
Fair use is a concept that applies exclusively to copyright, and allows you to backup copies of a work that you own (i.e. make personal copies), and use small4 portions of the work for educational or critical purposes, among other things. Fair use has been all but eliminated with the introduction of the DMCA, which gives legal credence to access control as opposed to copy protection, and makes circumvention of these access control measures illegal.5
With the exception of trade secrets, intellectual property is legally impossible to steal. It is only possible to steal a physical expression of intellectual property such as a book or a CD.
Copyright, patents and trademarks are infringed upon. Infringement does not fit the definition of theft or larceny. The key difference is that infringement does not deprive the original owner of the work; only of potential revenue associated with the work.
Equating the two makes the unfounded assumption that the consumer is presented with a choice between purchasing the work and obtaining an infringing copy. This is a false dilemma; in fact the third choice—doing neither—is the choice of honest citizens for whom the purchase is not a good value proposition. The difference is similar to that between cost and opportunity cost.
''When I use a word,'' Humpty Dumpty said, in a rather scornful tone, ''it means just what I choose it to mean—neither more nor less.''7
What the common usage of the term "Intellectual property" does is lump all of these different legal definitions in to one fuzzily-defined concept, ignoring all of the various exemptions and special cases for each specific type, unless they allow some new (more profitable) restriction to be applied.
Combined with the false analogy between ideas and property, and lots of hyperbole about 'stealing', the result of this is an ever-narrowing definition of what is permissible when you take someone else's work and use it. Copyright becomes an absolute, surrounded by a shrink-wrap license, and licensing becomes more and more restrictive.6
The logical conclusion of this hoarding attitude is that you the consumer do not own anything - you have a license to read this book, and a license to listen to that CD (twice (on Mondays)) - and that the physical material that changes hands - be it paper, a video or a DVD - is merely symbolic of a contractual agreement between you and the content owner.
A grim future, in my humble opinion.
If I've made any mistakes (gramatical, factual or otherwise) please let me know.
1: Here are clear examples of holders for each type of intellectual property. For copyright - the big five, who own most of the media outlets in the Western world. For patents - any big company with an R&D department, such as IBM. Trademarks - any conglomerate or fashion outlet (Levi, Dockers). Trade secrets - Coca-Cola, Kraft, Phillip Morris, etc.
2: Piracy is a term that was originally applied to printing houses who took an author's work and published it without their permission, in breach of copyright. The Lord of the Rings was first published in America by a pirate publishing house. More recently, a court decision regarding freelance journalism and online duplication rights has found the New York Times guilty of piracy.
3: Before the invention of the printing press, books were copied by hand. Known literature at the time was basically religious, and was disseminated by the Church, and transcribed (with varying degrees of accuracy) by monks.
4: For variable values of 'small'. For example, sampling a musical work in copyright requires explicit permission. When reviewing a film, there is a legally-defined maximum number of frames the critic of a film can use before requiring the permission of the copyright holder.
5: See DeCSS, Dmitry Sklyarov, SDMI, HDCP, WMA2, I could go on but it's really, really depressing, and nobody seems to care anyway.
6: The introduction of UCITA basically changes software sales into licensing deals (to quote legbagede at the aforementioned node).
7: Through the Looking Glass, Lewis Carroll, 1893
Thanks to Fisher for suggestions.