Another, less legalistic definition comes courtesy of the media lawyer Keith Schilling, the man who won pounds 100,000 damages, legal costs and an industry-shocking front-page apology from the Mail on Sunday for Brooke Shields. Schilling, who enjoys a celebrity client list and a Soho lifestyle more media than lawyer, says simply: "Libel is the sharp end of PR."
Unfortunately, it is not possible to elaborate on what he means by this as he refuses an interview without being granted copy approval, something The Independent, along with most papers, does not gladly give. He is concerned about client confidentiality. "I can't be giving an interview which may be portraying [my clients] in an unfavourable light," he says, kindly explaining that some people pay substantial fees for his services.
Yet Schilling, obviously not totally media shy, tempts me: if he is granted copy approval "it will be worth it".
Next he tries: "It won't be much of an article if I'm not there."
And finally, after an impasse has been reached: "I shall look forward to seeing your piece - `Hamlet without the Prince of Darkness' [sic]."
Schilling may see himself as a Prince of Darkness; others see him as a ruthless and spectacularly efficient media lawyer blazing a trail in a burgeoning legal art, one in which the worlds of celebrity, public relations and law are intertwined. The long-haired Schilling, 42 next month, certainly looks the part - more the ageing rock star than the chess-playing, Hampstead- dwelling lawyer that he is.
He founded his practice, Schilling & Lom and Partners, in 1984, eschewing a conventional City location for a W1 office, and since then has built up a celebrity client list that includes Michael Flatley, the Duchess of York, Liz Hurley, Bob Geldof and Chris Evans. Described by some as "a bit chippy" about his working-class background (he left Bromley Technical High at 16), he is known to prefer the Groucho and nights out clubbing to the drinks circuit of other media lawyers.
Professionally, too, he prefers to plough his own furrow. David Price, another top media lawyer, describes Schilling as "a bit different, not pompous and stuck-up, a breath of fresh air". But Schilling is no breath of fresh air for those on the receiving end of his libel threats. Like Oscar Beuselinck, the legendary libel lawyer he trained under, Schilling is renowned for his aggressive approach to litigation.
The Brooke Shields case, in which the Mail on Sunday printed a story about the French police questioning the Hollywood star on suspicion of drugs possession, was straightforward. It became obvious soon after the MoS published that the journalists involved had been duped. Most libel cases, though, are distinctly murkier, involving half-truths and complex debates about the meanings of words.
It makes no difference to Schilling. His approach, however clear-cut a case, is to attempt to leave editors, if not gibbering wrecks, then certainly cowering. One editor who received a Schilling letter said: "There wasn't that idea of gentlemanly fencing that you come to expect from legals. He really puts the boot in."
According to the Mirror editor Piers Morgan, Schilling is "a lethal operator, ruthless in his pursuit of the minutiae. From an editor's point of view he goes after the most ridiculous, trivial, inconsequential libels in the knowledge that we're unlikely to want to go to court and so will settle." Morgan says it is a worrying trend and one that ultimately will backfire on the celebrities as editors may opt to keep Schilling clients out of their papers.
Yet Morgan recently agreed a pounds 50,000 settlement to Liz Hurley after a Schilling intervention - which sounds anything but trivial.
Phil Hall, editor of the News of the World, regularly receives Schilling's missives. Two arrived within an hour of each other last week: one concerning a story about the comedian Craig Charles in which the News of the World claimed taped evidence; the other a story about Ulrika Jonsson which the paper had already dropped.
Says Hall, who can boast an editorship free of High Court appearances: "Certainly he does seem to shoot from the hip and have an American style of legal briefing in that he sends off a letter with a huge threat, very often before he knows all the evidence."
But the leading publicist Mark Borkowski has nothing but praise for Schilling. "He has a diligence and guile that makes journalists realise he means business. Depending on how high-profile your client is, there's a need on occasion to make sure their name is not being taken in vain. Keith demonstrates an ability on this level of work to make things happen."
Schilling was recommended to Brooke Shields by the PR Matthew Freud, and David Price, too, was introduced to the world of celebrity representation after being recommended by a PR. Says Price: "PR is a good source of work. They are concerned to protect their client's image and we talk about reputation, so it is very linked."
Another leading media lawyer, Mark Stephens, who represents among others Anthea Turner, Philip Schofield, Julian Clary and Jack Dee, speaks of the benefits of being media savvy.
"It may be that we work in conjunction with PR, but it tends to be that people come to me because I have an understanding of the media and I know the people involved - everybody from the editors downwards."
Such an intimate knowledge of Fleet Street is invaluable when it comes to crisis management. Stephens cites his handling of the Sun's exclusive on the Diana-James Hewitt affair.
Acting for Hewitt, he not only issued a writ but, talking of "scurrilous allegations of an improper relationship", announced its issue through the Press Association. Stephens knew it would take Sun lawyers at least 24 hours to get their hands on the actual writ and examine its contents, and correctly anticipated that the story would switch from the affair itself to speculation about whether Diana would have to give evidence in any forthcoming libel trial.
"By understanding the way in which a newspaper works and the timings that are crucial to it, or any news organisation, I was able to use that to my advantage to kill a story which my client didn't want."
However, as we all now know, the Major and the Princess were indeed having an "improper relationship".
Both Price and Stephens are keen to distance themselves from the tactical style of Schilling, but both also recognise the skills he displays and speak of the benefits of a small, intimate legal practice in which celebrities,increasingly happy to turn to the law, receive a personal service.
As the publicist Borkowski explains: "If you are a celebrity and become public property, you have to have many accoutrements. Those now include a media lawyer."