The runaway winner in the annual word of the year award, as decided by Oxford Dictionaries, an online site, is selfie, defined by the Oxford Dictionaries site as "a photograph that one has taken of oneself, typically with a smartphone or webcam and uploaded to a social media website".
Other contenders for the top spot were twerk (rauncy dancing), binge-watch (watching lots of television), and schmeat (synthetically produced meat from biological tissue), but, unusually this year, there was little argument, and selfie was the unanimous choice of the panel of judges.
The word of the year for 2013 does not have to have been coined in 2013, and, indeed, selfie first appeared, it is believed, on an Australian internet forum in 2002: “Um, drunk at a mates 21st, I tripped ofer [sic] and landed lip first (with front teeth coming a very close second) on a set of steps. I had a hole about 1cm long right through my bottom lip. And sorry about the focus, it was a selfie.” The word of the year does have to have achieved prominence in 2013, though, and given that the Pope was photographed being in someone's selfie, the activity and the word can certainly be said to have achieved prominence.
In the early days, the alternative spelling selfy was noted, but the -ie spelling is now de rigueur. The -y/-ie suffix usually denotes a diminutive or an endearing usage; the names Annie, Tommy, Betty, Danny etc are familiar, friendly forms. Barbie is a familiar form of barbecue; sickie, if not exactly friendly, is a slang and more informal way of saying a day's sick leave (usually not genuine). Many of the -ie words have an Australian origin, including selfie; Oxford Dictionaries says that "Australian English has something of a penchant for -ie words" and cites firie, firefighter, and tinnie, can of beer.
For more on selfie, its usage, and how it came to be chosen, see this Oxford Dictionaries piece.