Which Windows 7 edition is NOT available through retail and requires special Microsoft licensing?

Windows 7 Ultimate was the highest-end retail edition, combining features from Home Premium and Professional, and was available for purchase by individual consumers.

Windows 7 Professional was a retail edition targeting small businesses and power users, offering features like Remote Desktop and domain join capabilities, and was available for retail purchase.

Windows 7 Home Premium was a mainstream retail edition for home users, providing features for media and entertainment, and was widely available through retail channels.

Windows 7 Enterprise edition was specifically designed for large organizations and corporate environments, offering advanced features like BitLocker, DirectAccess, and AppLocker. This edition was only available through Microsoft Volume Licensing programs, meaning it could not be purchased as a standalone retail product.