Content library is one of the new feature introduced in VMware vSphere 6.0.
Content Library is a repository which can help manage templates and other files which are used in vCenter Server instances globally.
A single organization may have multiple vCenter Server instances across the globe and on these vCenter Server instance organization might have multiple templates, ISO images and various other files, which are independent of each other because of different versions that exist for these files on various vCenter Server instances.
With content library we can store OVF templates, ISO images and other types of files in a central location and publish them so as other content library can subscribe for the same.
One of the most important reason to use content library is sharing the content with other libraries and maintaining a consistency across.
Types of Content Library:
Local: local libraries are used to store items meant for single vCenter Server instance.
Published: A local library that is available for subscription.
Subscribed: Subscribed library is subscribed to publish library.
To ensure the contents of a subscribed library are up-to-date, the subscribed library automatically synchronizes to the published library.
You can use the option to download content from the source published library immediately or only when needed to manage your storage space.
During the synchronisation the library items that are new for the subscribed library are fully downloaded to the storage location of the subscribed library.
For more information kindly refer below