What is NZB?
NZB is a file format, used widely in Usenet.
It is XML document, which contains information about post and all parts of binary file.
Usually Usenet search engines use this file format, they create NZB file, which contains information about what has to be downloaded.
Traditional methods like downloading message headers are less efficient and slower than NZB concept.
Every Usenet post has "Message-ID" – unique identifier. When large binary file is uploaded via Usenet, it is divided into small messages, called segments or parts.
Such parts have their own Message-ID. NZB capable Usenet client simply reads NZB file and gets information about all needed Message-ID's, downloads them and makes binary file out of them.
yEnc or Uuencode decoding type is usually used. Nowadays people use yEnc.