A paparazzo is a celebrity photographer. You might see a paparazzo snapping pictures of your favorite pop singer as she stands in line at McDonald's.
A more common form of paparazzo is its plural, paparazzi. Either way, these nouns refer to photographers who photograph famous people and sell the photos to newspapers, magazines, and web sites. While there's no reason a paparazzo can't be respectful and professional, paparazzi are better known as obnoxious and pushy, invading celebrities' privacy in order to get candid pictures. The word comes from an Italian film, Fellini's "La Dolce Vita," and its photographer character, whose name is Paparazzo.