If you have been to a club, bar or health club here over the last month, you would have nodded along to the smash hit storming online music charts worldwide - you know, the one with that irresistible refrain: "Oppa - Gangnam Style!"

The tune, by eccentric South Korean dance-rapper Psy, has proven addictive; the accompanying video has gone viral faster than an epidemic. With the clip garnering 74 million YouTube hits (and counting) Gangnam is dead centre on the world's pop culture map.

But what is Gangnam? And what is Gangnam style?

That really depends on who you ask.

Gangnam is a district in Seoul that is full of South Korea's richest and most privileged, said Mr Robert Koehler, editor of Seoul magazine and a non-Gangnam resident. "Gangnam style means pretentious displays of wealth."

A consultant to the Presidential Council on National Branding, Ms Joanne Kim, said: "Across the country, people want to be part of Gangnam. It symbolises success."

Whether despised or aspirational, Gangnam means "south of the river", a reference to the Han River which bisects Seoul. It was all padi fields until the 1970s, when it was developed. Some of Seoul's most prestigious schools relocated to the district; ambitious parents followed. Real estate boomed in the 1980s; IT ventures soared in the 1990s.

"Gangnam is kind of nouveau riche; people made money from being on the right side of the property booms in the 1970s and 1980s," said Mike Breen, author of The Koreans, a book looking at Korea's history and development. "It is only one of Seoul's 25 districts, but represents something like 10 per cent of total Korean property values."

Ms Victoria Choi of real estate consultancy CBRE estimated that the average monthly rent for an office space in Gangnam works out to about US$2,100 (S$2,625) per sq ft.

Apartment prices are equally ludicrous: A two-bedroom apartment in Gangnam could buy you a European castle.

Gangnam is lined with coffee joints, restaurants and cinemas. The main road itself is usually jam-packed with traffic, making walking a better option than driving.

It also houses the offices of some of the top companies - South Korea's flagship conglomerate Samsung has its headquarters there.

At the end of a road filled with high-rise apartment and office towers lies COEX, a mega-complex encompassing an exhibition centre, shopping mall, aquarium, cineplex and a department store. It hosted G-20 leaders last year.

The Gangnam sub-districts of Cheongdam-dong and Apgujeong-dong are dubbed "Korea's Beverly Hills" and house the likes of Galleria, South Korea's priciest department store, as well as palatial restaurants, posh wine bars and exclusive night clubs. In recent years, Garuso-Gil, a street of al fresco bars, cafes and restaurants, has completed Gangnam's nightlife offerings.

This is the Gangnam Psy sings of - "Cool Korea", writ large.

Here, it is not enough to wear brand-name designer gear.

To qualify to be one of Gangnam's "beautiful people", you need a toned physique and chiselled features. The former is acquired at one of the area's huge gyms; the latter at the city's many cosmetic surgery clinics.

The joke in the video is Psy playing a bumpkin trying to be a Gangnam funkster. The song is more direct: It describes two normal Seoulites: Conservative and mild-mannered by day, hard partiers by night, and aspirants to be among Gangnam's chosen few.

But the song appears to take a dig at this desire by so many Koreans to be able to live the high life, even if it is beyond their means. In 2010, the average Korean household had debts of up to 155 per cent of its disposable income and every adult has, on average, five credit cards.

The video makes a social comment about the delusion many Koreans have in chasing after materialism.

For example, in the opening shots of the music video, Psy appears to be on a beach, but it turns out to be a mere playground instead. He shows off his dance moves, but rather than a swanky nightclub, does it in a bus-full of middle-aged people instead.

Psy, whose real name is Park Jae Sang, himself is not the typical pretty-boy crooner, but neither is he a struggling artist.

The son of an affluent businessman, he landed a cushy public job in lieu of his mandatory military service. However, unlike some stars who flee abroad when their call-up comes, Psy had integrity: When word leaked out, he voluntarily rejoined for a stint in the "real" army.

Psy's popularity was unaffected by that scandal, and now, in a nation desperate to promote itself internationally, he is a hero.

"We are surprised that this music video has been so popular in the US market because we had never done that before," said Mr Stephen Kwak of the Seoul Tourism Organisation. "Korean pop stars are quite famous in Asia, but not in the United States. Most of the Koreans are quite excited."

Mr Kwak's team plans to incorporate Gangnam Style in upcoming marketing events and commercials. Local media enthusiastically cover international coverage of the song.

But Gangnam is far from representative of South Korea where, in the run-up to December's presidential election, the key buzzwords are "wealth bipolarity" and "economic democratisation".

"It is Korea's dilemma; People envy Gangnam people, but at the same time, hate them," said Dr Kim Sung Soo, a social activist. "It's a love-hate relationship; everyone wants to be rich, but that is not possible."

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