Our perception of celebrities is that they are “somebody.”

 They are people who are celebrated in the media (TV, movies, the internet) for some reason. The reason might be something significant, or quite honestly, it might not be very significant at all.
There are different classes of celebrities. Some celebrities actually do things that are important, like Barack Obama or Hillary Clinton. Some are supremely talented like Barbra Streisand, Lance Armstrong or Tiger Woods. These people have talents that are notable; sports stars like Armstrong and Woods have books written about their athletic achievements. Streisand has made recordings and films. These people qualify as real, upper-echelon, certifiable celebrities.
Some celebrities, like Paris Hilton, are famous, but they don’t actually do very much. They are famous for being famous.
But there are still other types of celebrities. Sometimes a celebrity is famous because they are talented and also good-looking. When an extreme talent is combined with extreme good looks, the result can add up to a very glamorous celebrity. Someone, for example, like Jennifer “J-Lo” Lopez. J-Lo has a busy music career and also acts, but she is famous more than anything because she is quite pretty, glamorous, fashionable, and runs in circles that get a celebrity a lot of media attention. She is a well-dressed woman, and likely gets fashion ideas from all over — from Chanel to The Gap to Baby Phat.
At the farthest reaches of celebrity (the “supernova” type celebrity) are people who are really talented, (it helps if they have won an Academy Award or a Grammy) really good looking, and who do something unusual, like adopt a lot of children (Brad Pitt and Angelina Jolie), or get married a lot of times (Elizabeth Taylor). These “supernova” celebrities have so much going on, media, talent, and behavior-wise, they make it hard to look away. That’s the definition of a celebrity.