Cyberpunk definition in Encyclopaedia Britannica:

cyberpunk

A science-fiction subgenre characterized by countercultural antiheroes trapped in a dehumanized, high-tech future.

The word cyberpunk was coined by writer Bruce Bethke, who wrote a story with that title in 1982. He derived the term from the words cybernetics, the science of replacing human functions with computerized ones, and punk, the cacophonous music and nihilistic sensibility that developed in the youth culture during the 1970s and '80s. Science-fiction editor Gardner Dozois is generally credited with having popularized the term.

The roots of cyberpunk extend past Bethke's tale to the technological fiction of the 1940s and '50s, to the writings of Samuel R. Delany and others who took up themes of alienation in a high-tech future, and to the criticism of Bruce Sterling, who in the 1970s called for science fiction that addressed the social and scientific concerns of the day. Not until the publication of William Gibson's 1984 novel Neuromancer, however, did cyberpunk take off as a movement within the genre. Other members of the cyberpunk school include Sterling, John Shirley, and Rudy Rucker.

Cyberpunk definition in the Hacker's Jargon:

cyberpunk /si:'ber-puhnk/ /n.,adj./ A subgenre of SF launched in 1982 by William Gibson's epoch-making novel "Neuromancer" (though its roots go back through Vernor Vinge's "True Names" to John Brunner's 1975 novel "The Shockwave Rider"). Gibson's near-total ignorance of computers and the present-day hacker culture enabled him to speculate about the role of computers and hackers in the future in ways hackers have since found both irritatingly naive and tremendously stimulating. Gibson's work was widely imitated, in particular by the short-lived but innovative "Max Headroom" TV series.

Since 1990 or so, popular culture has included a movement or fashion trend that calls itself `cyberpunk', associated especially with the rave/techno subculture. Hackers have mixed feelings about this. On the one hand, self-described cyberpunks too often seem to be shallow trendoids in black leather who have substituted enthusiastic blathering about technology for actually learning and *doing* it. Attitude is no substitute for competence. On the other hand, at least cyberpunks are excited about the right things and properly respectful of hacking talent in those who have it. The general consensus is to tolerate them politely in hopes that they'll attract people who grow into being true hackers.

Cyberpunk definition in the old alt.cyberpunk FAQ:

Asking someone to define Cyberpunk is like asking someone to define art. Each person has their own ideas about what art is, what constitutes art and what doesn't. Yet we all still know art when we see it. The same is true for Cyberpunk - each cyberpunk has their own definition for it, yet common threads remain. In basic terms, these might be definied by an emphasis on individualism and technology (both in the present and in the future - and in the past as in The Difference Engine [a book by Gibson & Sterling]).

So what seperates cyberpunk from other types of sci-fi? Generally, cyberpunk occures in the not-so-distant-future. It generally occurs on earth, in a time where technology is prominent. Characters are generally "average Johnny Mnemonics" - not some fantastic hero with lots of virtue and a blinding smile. Cyberpunk revels in high-tech low-lifes, so you can expect to see lots of crime and back-stabbing and drugs and such. These are the basic elements of Gibsonesque CP (cyberpunk) - we've all seen it before in movies such as Blade Runner and TV Shows like Max Headroom.

In many cases, it appears as if our world is evolving into a classic cyberpunk setting: the rise of post-zaibatsu Japan with it's monopoly on technology, American cities developing into the "sprawl" (basically just large, mega-cities), drugs and crime are predominant in some cultures, and we thrive and survive on technology. So, it isn't too hard to see how cyberpunk evolved from being just a literary movement into a growing sub-culture - industrial and post-industrial aspects of the culture, virtual reality, rave parties, nootropics, computer hacking - they're all aspects of our culture, they all would fit nicely into a Gibson novel, and they all exist *now*.

So, what makes a cyberpunk? If you already knew all this stuff, and you're laughing at my generalities and inconsistencies, then you're definitely a cyberpunk. If you're a techno-junkie or an info-junkie, than you'd probably consider yourself a cyberpunk. Basically, if you live in a world in the not-so-distant-future, ahead of the masses (the masses being guys named Buford who sit out in front of their trailer homes in lawn chairs sipping a Bud and watching the Indy 500 on an old tv), then you could probably safely consider yourself a cyberpunk. It's a spectrum, though - I mean, it's kind of like if Michelangelo had an assistant, he would probably not consider the assistant an artist. Yet to his friends and family, that assistant may seem like a great artist. I consider myself a cyberpunk compared to the masses that walk the halls of my school, yet at a virtual reality conference in the presence of the likes of Jaron Lanier, Gibson, John Perry Barlow, Timothy Leary, RU Sirius, etc. I would probably be more hesitant in labeling myself a true cyberpunk. But one the beauties of CP is that it is still somewhat elitist to an extent: members of the community realize that we who walk on the fringes of culture need to hold each others' hand until the masses join us - the communal atmosphere, at times, can be seen as similair to the early hippie movement of the late 50's/early 60's.