Photojournalism is a style of photography that is meant to capture news through a camera. This is typically an unforgiving look at whatever event is occurring at the time, and it is meant to be raw, truthful and vivid - sometimes, heartbreakingly so.
In photojournalism, everyday events are captured on camera with intent to educate and inform, and as a way of communicating with an unbiased point of view.
Photojournalism once was used as a serious news form, and the only purpose was to provide a visual supplement to a hard news story covered by a reporter. Nowadays, photojournalism is at an all-time extreme, with the purpose extending to covering the lifestyles of celebrities and the rich and famous. While one might argue that the paparazzi antics are hardly considered 'photojournalism', the traditional rules are still applicable: pictures being caught on camera to educate and inform.