What is an NZB File?
A list of files Usenet software can use for downloading.
NZB files list a group of posts that you want to download from Usenet. Most often, they list all of the parts of a single file you want to download. It doesn't sounds as powerful as it is, but imagine a 4 Gigabyte video that you want to download. If it was uploaded in 1 Megabyte blocks then that is in 4,000 actual pieces! Your news reader will just combine all of these and show you 1 listing for the single file that it really is, but what if you wanted to tell someone else about it? Better yet, what if you wanted to use a Usenet search engine, or Usenet Indexer, to find a file you liked and have your news reader software download it? That Usenet search engine needs to be able to give you something to help your news reader find those 4,000 pieces. That something is an NZB file.
So, your friend sent you an NZB file for a great post, or you found something on a Usenet search engine that looks interesting and you downloaded the NZB file from them. It's a thin little file that looks almost readable if you opened it. You now give this to your Usenet software, and it will download everything automatically. Sometimes this is done by just double-clicking on it and other times you will need to click on a button in your software to tell it to open the NZB file, this just varies depending on what Usenet software you are using.
NZB files provide an easy way to tell other people about large files posted to Usenet. They aren't the files themselves, but a condensed list of them that your news reader can use to get the actual file(s). Once you give the NZB file to your Usenet software, the process is totally hands off and as automatic as if you had double clicked on something to download from a newsgroup.
As you can see, they make web based Usenet search engines and indexers possible.