Here you can find information regarding the Gross and the Net media usage.
 
The Gross media represents the total media used by the job, including the media used by marks, labels or bleeds, as well as the wasted media on which nothing is printed. The Gross media is more explicitly represented in the image below, by the red outline.
The Net media represents the final print of the job. The net media is more explicitly represented in the image below, by the red outline.
Also, when having overlapping jobs, or more than one job on the media, the Net media usage will be calculated as presented in the image below: