The site must be a NZB search engine or indexer, or should contain valuable information about this open standard. Submitting a site in a wrong category may delay its review a lot.
The acronym NZB comes from NewZBin, the name of the company that developed this open standard. Basically, a NZB file contains all the necessary information about parts of a binary file on a newsgroup, making downloading of thousands of headers unnecessary. When fed to a compatible newsreader, this newsreader will automatically retrieve relevant messages only, and combine and decode the desired file. The user often needs to merely look for a file on an automated NZB indexer, download the corresponding NZB file and open it with the newsreader. All the rest is fully automated.