AKA MSDN. MicrosoftCorporation's subscription-based service for developers.

MicroSoftDeveloperNetwork includes two main features:

1. technical support, tutorial and demo materials form various MicrosoftCorporation WebSites shipped on CD or DVD so developers can install and consult it locally. Sufficiently highly-paying customers can even install it on a LAN for all developers within an organisation.
2. access to support forums in which developers are guarranteed an answer. Usefulness and meaningfulness of the answers are not guarranteed.

MicroSoftDeveloperNetwork is almost always bundled with other products, typically various OperatingSystems and VisualStudio packages.

See: http://msdn.microsoft.com/