A selfie is a photo someone takes of themselves, usually on a smartphone. Often they are snapped in front of a mirror for ease of framing, and in the twitterverse they are uploaded thick and fast. There need be no particular context for a selfie. They are not generally photos of people on holidays or doing something out of the ordinary, they are essentially self-portraits shared with anyone who cares to view them using social media.

Posting selfies has become so common among some young people that the Wall Street Journal recently ran a story on how to take a great selfie, with advice from popular accessories blogger Tina Craig, of Bag Snob fame. She suggests facing your phone directly rather than using a mirror, and if you are after a head shot, to let your face and hair fill the screen.

And as with most trends that take off among young people, it has not taken long for advertising executives to jump onboard. Lingerie brand Bendon recently launched a campaign called Selfies with Besties, encouraging young women to take a selfie with their best friend and post it on Twitter, Facebook or Instagram to win prizes.

''Selfies. Don't pretend you don't know what they are. They are the self portraits taken by girls, guys, celebs (and probably your fine self) on a camera phone and uploaded to Instagram, Facebook and Twitter for all the world to see,'' their campaign web page reads.

Australian Olympic swimmer Stephanie Rice caused a stir when she posted two selfies earlier this year, both showing off her athlete's figure in designer bikinis while keeping her face covered. Rice sparked a debate online over whether the selfie is an example of narcissism, a canny tool for self-promotion or just a demonstration of healthy and confident body image.

Lubna Alam, a social media expert at The University of Canberra, says there is no real logic to the selfie. Rather, it is driven by a combination of social factors. There is an element of self-promotion, to be sure. What used to be the domain of the famous is now popular amongst ordinary people.

''It's just a platform to showcase yourself, and it's free, so now you can be a celebrity for a day,'' she says.

The importance of SMS and social media in day-to-day life can also go some way to explaining the selfie, as these methods of communication have become so common that sharing pictures of yourself online no longer seems a strange thing to do.

Alam says it has got to do with social learning and social comparison. We learn what to do from our friends. ''If everyone is doing it, it must be fun, it's cheeky, fun and cool,'' she said.

But it is also a phenomenon that is very much tied to youth. Generation Y, Alam says, is more comfortable sharing information online than older people.

''The baby boomers and generation X, they were more worried about their reputations, whereas generation Y, the new digital natives, their attitude is quite different,'' she said.

Alam says those in their teens and twenties were more likely to view social media use in terms of how it could benefit them, and therefore take more risks with their online personas.

She says they sometimes fail to recognise the permanence of their actions online. Many adults have cringe-worthy memories of their teenage years, but this generation of adolescents will not be able to so easily leave those times in the past.

''They don't understand that everything they do online is published for life,'' she said.

But young people are not completely oblivious to potential dangers of damage to reputation, unwanted contact and stalkers. Rather, Alam says there is disparity between the risks they perceive and how they behave. When they see their network of friends acting in a certain way without negative consequences they become more comfortable doing the same thing.

She would like to see social media education made mandatory in schools, and she thinks it is important to start that process while students are still young.

''This is a fundamental way for them to communicate,'' she said.

There is something fascinating about the selfie as an insight into exactly how the young people involved would like to be seen. They are intimate self-portraits, and yet they're artificial. It is common for those posting selfies to make a comment about being bored, making what they are doing seem nonchalant, and yet they usually seem to be posed.