Depth reporting is what makes readers aware of all aspects of a given subject by giving them all possible information, including background and atmosphere.
Depth reporting treats a story with a kind of thoroughness of details and background that a 300-words story cannot. It tells the reader not only what happened but why it happened.
Depth reporting is simply good reporting with an eye for accuracy and detail.
Depth reporting is digging beneath the surface and coming up with facts that aren’t immediately visible, but which nevertheless contribute to an understanding of story.